Create Excel Files in Azure App Service Linux with Excel Library

14 Aug 202624 minutes to read

.NET Excel Library for ASP.NET Core platform can be used to create, read, and edit Excel files in Azure App Service on Linux.

Prerequisites

Before you begin, ensure the following:

• An active Azure subscription. If you do not have one, see Create an Azure account.
• A Syncfusion license key. Register it in Program.cs (see the snippet in Step 4a below) or via the SyncfusionLicense.txt file. In Azure App Service on Linux, the recommended approach is to store the key in an environment variable or application setting and load it at startup see the Syncfusion licensing overview.

Create a simple Excel report

The steps below illustrate creating a simple invoice-formatted Excel document in Azure App Service on Linux.

Step 1: Create a new ASP.NET Core Web Application (Model-View-Controller).

Step 2: Name the project.

Step 3: Select the framework and click the Create button.

Step 4: Install the Syncfusion.XlsIO.Net.Core NuGet package as a reference to your .NET Standard application from NuGet.org.

NOTE

Starting with v16.2.0.x, if you reference Syncfusion^® assemblies from trial setup or from the NuGet feed, you also have to add “Syncfusion.Licensing” assembly reference and include a license key in your projects. Please refer to this link to know about registering Syncfusion^® license key in your applications to use our components.

Step 4a: Register your Syncfusion license key in Program.cs (before app.Run()). Replace the placeholder with your actual key.

C#

Syncfusion.Licensing.SyncfusionLicenseProvider.RegisterLicense("YOUR_LICENSE_KEY");

For production deployments to Azure App Service on Linux, store the key in an App Service Application Setting (for example, SYNCFUSION_LICENSE_KEY) and read it via Environment.GetEnvironmentVariable so the key is not committed to source control.

Step 5: Include the following namespaces in HomeController.cs.

C#

using Syncfusion.XlsIO;
   using System.IO;
   using Syncfusion.Drawing;

VB.NET

Imports Syncfusion.XlsIO
   Imports System.IO
   Imports Syncfusion.Drawing

Step 5a: Inject IWebHostEnvironment into HomeController so the logo file path can be resolved at runtime. Add a constructor parameter and a private field:

C#

private readonly IWebHostEnvironment _hostingEnvironment;

public HomeController(IWebHostEnvironment hostingEnvironment)
{
    _hostingEnvironment = hostingEnvironment;
}

The code below uses _hostingEnvironment.WebRootPath to resolve the logo path; if you prefer a different name, adjust the field accordingly.

Step 6: Add a new button in the Index.cshtml as shown below.

CSHTML

@{Html.BeginForm("CreateDocument", "Home", FormMethod.Get);
       {
           <div>
               <input type="submit" value="Create Document" style="width:150px;height:27px" />
           </div>
       }
       Html.EndForm();
   }

Step 7: Add the following code snippet in HomeController.cs (the body of the CreateDocument action) to create an Excel file and download it.

C#

//Create an instance of ExcelEngine
   using (ExcelEngine excelEngine = new ExcelEngine())
   {
     IApplication application = excelEngine.Excel;  
     application.DefaultVersion = ExcelVersion.Xlsx;
     
     //Create a workbook
     IWorkbook workbook = application.Workbooks.Create(1);
     IWorksheet worksheet = workbook.Worksheets[0];
   
     //Adding a picture (place AdventureCycles-Logo.png in wwwroot/ and resolve via IWebHostEnvironment.WebRootPath)
     using (FileStream imageStream = new FileStream(Path.Combine(_hostingEnvironment.WebRootPath, "AdventureCycles-Logo.png"), FileMode.Open, FileAccess.Read))
     {
       IPictureShape shape = worksheet.Pictures.AddPicture(1, 1, imageStream, 20, 20);
     }
     
     //Disable gridlines in the worksheet
     worksheet.IsGridLinesVisible = false;
     
     //Enter values to the cells from A3 to A5
     worksheet.Range["A3"].Text = "46036 Michigan Ave";
     worksheet.Range["A4"].Text = "Canton, USA";
     worksheet.Range["A5"].Text = "Phone: [phone]";
     
     //Make the text bold
     worksheet.Range["A3:A5"].CellStyle.Font.Bold = true;
     
     //Merge cells
     worksheet.Range["D1:E1"].Merge();
     
     //Enter text to the cell D1 and apply formatting.
     worksheet.Range["D1"].Text = "INVOICE";
     worksheet.Range["D1"].CellStyle.Font.Bold = true;
     worksheet.Range["D1"].CellStyle.Font.RGBColor = Color.FromArgb(42, 118, 189);
     worksheet.Range["D1"].CellStyle.Font.Size = 35;
     
     //Apply alignment in the cell D1
     worksheet.Range["D1"].CellStyle.HorizontalAlignment = ExcelHAlign.HAlignRight;
     worksheet.Range["D1"].CellStyle.VerticalAlignment = ExcelVAlign.VAlignTop;
     
     //Enter values to the cells from D5 to E8
     worksheet.Range["D5"].Text = "INVOICE#";
     worksheet.Range["E5"].Text = "DATE";
     worksheet.Range["D6"].Number = 1028;
     worksheet.Range["E6"].Value = "12/31/2018";
     worksheet.Range["D7"].Text = "CUSTOMER ID";
     worksheet.Range["E7"].Text = "TERMS";
     worksheet.Range["D8"].Number = 564;
     worksheet.Range["E8"].Text = "Due Upon Receipt";
     
     //Apply RGB backcolor to the cells from D5 to E8
     worksheet.Range["D5:E5"].CellStyle.Color = Color.FromArgb(42, 118, 189);
     worksheet.Range["D7:E7"].CellStyle.Color = Color.FromArgb(42, 118, 189);
     
     //Apply known colors to the text in cells D5 to E8
     worksheet.Range["D5:E5"].CellStyle.Font.Color = ExcelKnownColors.White;
     worksheet.Range["D7:E7"].CellStyle.Font.Color = ExcelKnownColors.White;
     
     //Make the text as bold from D5 to E8
     worksheet.Range["D5:E8"].CellStyle.Font.Bold = true;
     
     //Apply alignment to the cells from D5 to E8
     worksheet.Range["D5:E8"].CellStyle.HorizontalAlignment = ExcelHAlign.HAlignCenter;
     worksheet.Range["D5:E5"].CellStyle.VerticalAlignment = ExcelVAlign.VAlignCenter;
     worksheet.Range["D7:E7"].CellStyle.VerticalAlignment = ExcelVAlign.VAlignCenter;
     worksheet.Range["D6:E6"].CellStyle.VerticalAlignment = ExcelVAlign.VAlignTop;
     
     //Enter value and applying formatting in the cell A7
     worksheet.Range["A7"].Text = "  BILL TO";
     worksheet.Range["A7"].CellStyle.Color = Color.FromArgb(42, 118, 189);
     worksheet.Range["A7"].CellStyle.Font.Bold = true;
     worksheet.Range["A7"].CellStyle.Font.Color = ExcelKnownColors.White;
     
     //Apply alignment
     worksheet.Range["A7"].CellStyle.HorizontalAlignment = ExcelHAlign.HAlignLeft;
     worksheet.Range["A7"].CellStyle.VerticalAlignment = ExcelVAlign.VAlignCenter;
     
     //Enter values in the cells A8 to A12
     worksheet.Range["A8"].Text = "Steyn";
     worksheet.Range["A9"].Text = "Great Lakes Food Market";
     worksheet.Range["A10"].Text = "20 Whitehall Rd";
     worksheet.Range["A11"].Text = "North Muskegon,USA";
     worksheet.Range["A12"].Text = "[phone]";
     
     //Create a Hyperlink for e-mail in the cell A13
     IHyperLink hyperlink = worksheet.HyperLinks.Add(worksheet.Range["A13"]);
     hyperlink.Type = ExcelHyperLinkType.Url;
     hyperlink.Address = "[email protected]";
     hyperlink.ScreenTip = "Send Mail";
     
     //Merge column A and B from row 15 to 22
     worksheet.Range["A15:B15"].Merge();
     worksheet.Range["A16:B16"].Merge();
     worksheet.Range["A17:B17"].Merge();
     worksheet.Range["A18:B18"].Merge();
     worksheet.Range["A19:B19"].Merge();
     worksheet.Range["A20:B20"].Merge();
     worksheet.Range["A21:B21"].Merge();
     worksheet.Range["A22:B22"].Merge();
     
     //Enter details of products and prices
     worksheet.Range["A15"].Text = "  DESCRIPTION";
     worksheet.Range["C15"].Text = "QTY";
     worksheet.Range["D15"].Text = "UNIT PRICE";
     worksheet.Range["E15"].Text = "AMOUNT";
     worksheet.Range["A16"].Text = "Cabrales Cheese";
     worksheet.Range["A17"].Text = "Chocos";
     worksheet.Range["A18"].Text = "Pasta";
     worksheet.Range["A19"].Text = "Cereals";
     worksheet.Range["A20"].Text = "Ice Cream";
     worksheet.Range["C16"].Number = 3;
     worksheet.Range["C17"].Number = 2;
     worksheet.Range["C18"].Number = 1;
     worksheet.Range["C19"].Number = 4;
     worksheet.Range["C20"].Number = 3;
     worksheet.Range["D16"].Number = 21;
     worksheet.Range["D17"].Number = 54;
     worksheet.Range["D18"].Number = 10;
     worksheet.Range["D19"].Number = 20;
     worksheet.Range["D20"].Number = 30;
     worksheet.Range["D23"].Text = "Total";
     
     //Apply number format
     worksheet.Range["D16:E22"].NumberFormat = "$0.00";
     worksheet.Range["E23"].NumberFormat = "$0.00";
     
     //Apply incremental formula for column Amount by multiplying Qty and UnitPrice
     application.EnableIncrementalFormula = true;
     worksheet.Range["E16:E20"].Formula = "=C16*D16";
     
     //Formula for Sum the total
     worksheet.Range["E23"].Formula = "=SUM(E16:E22)";
     
     //Apply borders
     worksheet.Range["A16:E22"].CellStyle.Borders[ExcelBordersIndex.EdgeTop].LineStyle = ExcelLineStyle.Thin;
     worksheet.Range["A16:E22"].CellStyle.Borders[ExcelBordersIndex.EdgeBottom].LineStyle = ExcelLineStyle.Thin;
     worksheet.Range["A16:E22"].CellStyle.Borders[ExcelBordersIndex.EdgeTop].Color = ExcelKnownColors.Grey_25_percent;
     worksheet.Range["A16:E22"].CellStyle.Borders[ExcelBordersIndex.EdgeBottom].Color = ExcelKnownColors.Grey_25_percent;
     worksheet.Range["A23:E23"].CellStyle.Borders[ExcelBordersIndex.EdgeTop].LineStyle = ExcelLineStyle.Thin;
     worksheet.Range["A23:E23"].CellStyle.Borders[ExcelBordersIndex.EdgeBottom].LineStyle = ExcelLineStyle.Thin;
     worksheet.Range["A23:E23"].CellStyle.Borders[ExcelBordersIndex.EdgeTop].Color = ExcelKnownColors.Black;
     worksheet.Range["A23:E23"].CellStyle.Borders[ExcelBordersIndex.EdgeBottom].Color = ExcelKnownColors.Black;
     
     //Apply font setting for cells with product details
     worksheet.Range["A3:E23"].CellStyle.Font.FontName = "Arial";
     worksheet.Range["A3:E23"].CellStyle.Font.Size = 10;
     worksheet.Range["A15:E15"].CellStyle.Font.Color = ExcelKnownColors.White;
     worksheet.Range["A15:E15"].CellStyle.Font.Bold = true;
     worksheet.Range["D23:E23"].CellStyle.Font.Bold = true;
     
     //Apply cell color
     worksheet.Range["A15:E15"].CellStyle.Color = Color.FromArgb(42, 118, 189);
     
     //Apply alignment to cells with product details
     worksheet.Range["A15"].CellStyle.HorizontalAlignment = ExcelHAlign.HAlignLeft;
     worksheet.Range["C15:C22"].CellStyle.HorizontalAlignment = ExcelHAlign.HAlignCenter;
     worksheet.Range["D15:E15"].CellStyle.HorizontalAlignment = ExcelHAlign.HAlignCenter;
     
     //Apply row height and column width to look good
     worksheet.Range["A1"].ColumnWidth = 36;
     worksheet.Range["B1"].ColumnWidth = 11;
     worksheet.Range["C1"].ColumnWidth = 8;
     worksheet.Range["D1:E1"].ColumnWidth = 18;
     worksheet.Range["A1"].RowHeight = 47;
     worksheet.Range["A2"].RowHeight = 15;
     worksheet.Range["A3:A4"].RowHeight = 15;
     worksheet.Range["A5"].RowHeight = 18;
     worksheet.Range["A6"].RowHeight = 29;
     worksheet.Range["A7"].RowHeight = 18;
     worksheet.Range["A8"].RowHeight = 15;
     worksheet.Range["A9:A14"].RowHeight = 15;
     worksheet.Range["A15:A23"].RowHeight = 18;  
     
     //Saving the Excel to the MemoryStream 
     MemoryStream stream = new MemoryStream();  
     workbook.SaveAs(stream);
     
     //Set the position as '0'.
     stream.Position = 0;
     
     //Download the Excel file in the browser
     FileStreamResult fileStreamResult = new FileStreamResult(stream, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");  
     fileStreamResult.FileDownloadName = "Output.xlsx";  
     return fileStreamResult;
   }

VB.NET

'Create an instance of ExcelEngine
   Using excelEngine As ExcelEngine = New ExcelEngine()
   
     Dim application As IApplication = excelEngine.Excel  
     application.DefaultVersion = ExcelVersion.Xlsx
     
     'Create a workbook
     Dim workbook As IWorkbook = application.Workbooks.Create(1)
     Dim worksheet As IWorksheet = workbook.Worksheets(0)
     
     'Adding a picture
     Dim imageStream As FileStream = New FileStream("AdventureCycles-Logo.png", FileMode.Open, FileAccess.Read)
     Dim shape As IPictureShape = worksheet.Pictures.AddPicture(1, 1, imageStream, 20, 20)
     
     'Disable gridlines in the worksheet
     worksheet.IsGridLinesVisible = False
     
     'Enter values to the cells from A3 to A5
     worksheet.Range("A3").Text = "46036 Michigan Ave"
     worksheet.Range("A4").Text = "Canton, USA"
     worksheet.Range("A5").Text = "Phone: [phone]"
     
     'Make the text bold
     worksheet.Range("A3:A5").CellStyle.Font.Bold = True
     
     'Merge cells
     worksheet.Range("D1:E1").Merge()
     
     'Enter text to the cell D1 and apply formatting.
     worksheet.Range("D1").Text = "INVOICE"
     worksheet.Range("D1").CellStyle.Font.Bold = True
     worksheet.Range("D1").CellStyle.Font.RGBColor = Color.FromArgb(42, 118, 189)
     worksheet.Range("D1").CellStyle.Font.Size = 35
     
     'Apply alignment in the cell D1
     worksheet.Range("D1").CellStyle.HorizontalAlignment = ExcelHAlign.HAlignRight
     worksheet.Range("D1").CellStyle.VerticalAlignment = ExcelVAlign.VAlignTop
     
     'Enter values to the cells from D5 to E8
     worksheet.Range("D5").Text = "INVOICE#"
     worksheet.Range("E5").Text = "DATE"
     worksheet.Range("D6").Number = 1028
     worksheet.Range("E6").Value = "12/31/2018"
     worksheet.Range("D7").Text = "CUSTOMER ID"
     worksheet.Range("E7").Text = "TERMS"
     worksheet.Range("D8").Number = 564
     worksheet.Range("E8").Text = "Due Upon Receipt"
     
     'Apply RGB back color to the cells from D5 to E8
     worksheet.Range("D5:E5").CellStyle.Color = Color.FromArgb(42, 118, 189)
     worksheet.Range("D7:E7").CellStyle.Color = Color.FromArgb(42, 118, 189)
     
     'Apply known colors to the text in cells D5 to E8
     worksheet.Range("D5:E5").CellStyle.Font.Color = ExcelKnownColors.White
     worksheet.Range("D7:E7").CellStyle.Font.Color = ExcelKnownColors.White
     
     'Make the text as bold from D5 to E8
     worksheet.Range("D5:E8").CellStyle.Font.Bold = True
     
     'Apply alignment to the cells from D5 to E8
     worksheet.Range("D5:E8").CellStyle.HorizontalAlignment = ExcelHAlign.HAlignCenter
     worksheet.Range("D5:E5").CellStyle.VerticalAlignment = ExcelVAlign.VAlignCenter
     worksheet.Range("D7:E7").CellStyle.VerticalAlignment = ExcelVAlign.VAlignCenter
     worksheet.Range("D6:E6").CellStyle.VerticalAlignment = ExcelVAlign.VAlignTop
     
     'Enter value and applying formatting in the cell A7
     worksheet.Range("A7").Text = "  BILL TO"
     worksheet.Range("A7").CellStyle.Color = Color.FromArgb(42, 118, 189)
     worksheet.Range("A7").CellStyle.Font.Bold = True
     worksheet.Range("A7").CellStyle.Font.Color = ExcelKnownColors.White
     
     'Apply alignment
     worksheet.Range("A7").CellStyle.HorizontalAlignment = ExcelHAlign.HAlignLeft
     worksheet.Range("A7").CellStyle.VerticalAlignment = ExcelVAlign.VAlignCenter
     
     'Enter values in the cells A8 to A12
     worksheet.Range("A8").Text = "Steyn"
     worksheet.Range("A9").Text = "Great Lakes Food Market"
     worksheet.Range("A10").Text = "20 Whitehall Rd"
     worksheet.Range("A11").Text = "North Muskegon,USA"
     worksheet.Range("A12").Text = "[phone]"
     
     'Create a Hyperlink for e-mail in the cell A13
     Dim hyperlink As IHyperLink = worksheet.HyperLinks.Add(worksheet.Range("A13"))
     hyperlink.Type = ExcelHyperLinkType.Url
     hyperlink.Address = "[email protected]"
     hyperlink.ScreenTip = "Send Mail"
     
     'Merge column A and B from row 15 to 22
     worksheet.Range("A15:B15").Merge()
     worksheet.Range("A16:B16").Merge()
     worksheet.Range("A17:B17").Merge()
     worksheet.Range("A18:B18").Merge()
     worksheet.Range("A19:B19").Merge()
     worksheet.Range("A20:B20").Merge()
     worksheet.Range("A21:B21").Merge()
     worksheet.Range("A22:B22").Merge()
     
     'Enter details of products and prices
     worksheet.Range("A15").Text = "  DESCRIPTION"
     worksheet.Range("C15").Text = "QTY"
     worksheet.Range("D15").Text = "UNIT PRICE"
     worksheet.Range("E15").Text = "AMOUNT"
     worksheet.Range("A16").Text = "Cabrales Cheese"
     worksheet.Range("A17").Text = "Chocos"
     worksheet.Range("A18").Text = "Pasta"
     worksheet.Range("A19").Text = "Cereals"
     worksheet.Range("A20").Text = "Ice Cream"
     worksheet.Range("C16").Number = 3
     worksheet.Range("C17").Number = 2
     worksheet.Range("C18").Number = 1
     worksheet.Range("C19").Number = 4
     worksheet.Range("C20").Number = 3
     worksheet.Range("D16").Number = 21
     worksheet.Range("D17").Number = 54
     worksheet.Range("D18").Number = 10
     worksheet.Range("D19").Number = 20
     worksheet.Range("D20").Number = 30
     worksheet.Range("D23").Text = "Total"
     
     'Apply number format
     worksheet.Range("D16:E22").NumberFormat = "$0.00"
     worksheet.Range("E23").NumberFormat = "$0.00"
     
     'Apply incremental formula for column Amount by multiplying Qty and UnitPrice
     application.EnableIncrementalFormula = True
     worksheet.Range("E16:E20").Formula = "=C16*D16"
     
     'Formula for Sum the total
     worksheet.Range("E23").Formula = "=SUM(E16:E22)"
     
     'Apply borders
     worksheet.Range("A16:E22").CellStyle.Borders(ExcelBordersIndex.EdgeTop).LineStyle = ExcelLineStyle.Thin
     worksheet.Range("A16:E22").CellStyle.Borders(ExcelBordersIndex.EdgeBottom).LineStyle = ExcelLineStyle.Thin
     worksheet.Range("A16:E22").CellStyle.Borders(ExcelBordersIndex.EdgeTop).Color = ExcelKnownColors.Grey_25_percent
     worksheet.Range("A16:E22").CellStyle.Borders(ExcelBordersIndex.EdgeBottom).Color = ExcelKnownColors.Grey_25_percent
     worksheet.Range("A23:E23").CellStyle.Borders(ExcelBordersIndex.EdgeTop).LineStyle = ExcelLineStyle.Thin
     worksheet.Range("A23:E23").CellStyle.Borders(ExcelBordersIndex.EdgeBottom).LineStyle = ExcelLineStyle.Thin
     worksheet.Range("A23:E23").CellStyle.Borders(ExcelBordersIndex.EdgeTop).Color = ExcelKnownColors.Black
     worksheet.Range("A23:E23").CellStyle.Borders(ExcelBordersIndex.EdgeBottom).Color = ExcelKnownColors.Black
     
     'Apply font setting for cells with product details
     worksheet.Range("A3:E23").CellStyle.Font.FontName = "Arial"
     worksheet.Range("A3:E23").CellStyle.Font.Size = 10
     worksheet.Range("A15:E15").CellStyle.Font.Color = ExcelKnownColors.White
     worksheet.Range("A15:E15").CellStyle.Font.Bold = True
     worksheet.Range("D23:E23").CellStyle.Font.Bold = True
     
     'Apply cell color
     worksheet.Range("A15:E15").CellStyle.Color = Color.FromArgb(42, 118, 189)
     
     'Apply alignment to cells with product details
     worksheet.Range("A15").CellStyle.HorizontalAlignment = ExcelHAlign.HAlignLeft
     worksheet.Range("C15:C22").CellStyle.HorizontalAlignment = ExcelHAlign.HAlignCenter
     worksheet.Range("D15:E15").CellStyle.HorizontalAlignment = ExcelHAlign.HAlignCenter
     
     'Apply row height and column width to look good
     worksheet.Range("A1").ColumnWidth = 36
     worksheet.Range("B1").ColumnWidth = 11
     worksheet.Range("C1").ColumnWidth = 8
     worksheet.Range("D1:E1").ColumnWidth = 18
     worksheet.Range("A1").RowHeight = 47
     worksheet.Range("A2").RowHeight = 15
     worksheet.Range("A3:A4").RowHeight = 15
     worksheet.Range("A5").RowHeight = 18
     worksheet.Range("A6").RowHeight = 29
     worksheet.Range("A7").RowHeight = 18
     worksheet.Range("A8").RowHeight = 15
     worksheet.Range("A9:A14").RowHeight = 15
     worksheet.Range("A15:A23").RowHeight = 18
     
     'Saving the Excel to the MemoryStream 			
     Dim stream As MemoryStream = New MemoryStream()
     workbook.SaveAs(stream)
     
     'Set the position as '0'.
     stream.Position = 0
     
     'Download the Excel file in the browser
     Dim fileStreamResult As FileStreamResult = New FileStreamResult(stream, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet")
     fileStreamResult.FileDownloadName = "Output.xlsx"
     Return fileStreamResult
   End Using

Steps to publish to Azure App Service on Linux

Step 1: Right-click the project and select Publish option.

Step 2: Select the publish target as Azure.

Step 3: Select the Specific target as Azure App Service (Linux).

Step 4: To create a new app service, click Create new option.

Step 5: Click the Create button to proceed with App Service creation.

Step 6: Click the Finish button to finalize the App Service creation.

Step 7: Click Close button.

Step 8: Click the Publish button.

Step 9: The publish operation has succeeded.

Step 10: The published web page opens in the browser.

Step 11: Click Create Document to create a simple Excel document. The output Excel document is shown below.

A complete working example of how to create an Excel file in Azure App Service on Linux in C# is present on this GitHub page.

Read and Edit an Excel File

The following code snippet illustrates how to read and edit an Excel file in Azure App Service on Linux.

Step 1: Add a sample Excel file named Sample.xlsx to the wwwroot/ folder of the project (right-click wwwroot -> Add -> New Item -> Excel Workbook, or drag-and-drop the file). Set its Build Action to Content and Copy to Output Directory to Copy if newer so it is deployed with the App Service.

C#

//New instance of ExcelEngine is created.
//Equivalent to launching Microsoft Excel with no workbooks open.
using (ExcelEngine excelEngine = new ExcelEngine())
{
  //Instantiate the Excel application object
  IApplication application = excelEngine.Excel;

//Assigns default application version
application.DefaultVersion = ExcelVersion.Xlsx;

//A existing workbook is opened.             
IWorkbook workbook = application.Workbooks.Open("Sample.xlsx");

//Access first worksheet from the workbook.
IWorksheet worksheet = workbook.Worksheets[0];

//Set Text in cell A3.
worksheet.Range["A3"].Text ="Hello World";

//Access a cell value from Excel
var value = worksheet.Range["A1"].Value;

//Defining the ContentType for excel file.
string ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";

//Define the file name.
string fileName = "Output.xlsx";

//Creating stream object.
MemoryStream stream = new MemoryStream();

//Saving the workbook to stream in XLSX format
workbook.SaveAs(stream);

stream.Position = 0;

//The ExcelEngine is disposed automatically by the using block above.
//Creates a FileContentResult object by using the file contents, content type, and file name.
return File(stream, ContentType, fileName);
}

A complete working example of how to read and edit an Excel file in Azure App Service on Linux in C# is present on this GitHub page.

Click here to explore the rich set of Syncfusion^® Excel library (XlsIO) features.

An online sample link to create an Excel document in ASP.NET Core.