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OCR PDFs Using Syncfusion Web API

26 Mar 202611 minutes to read

The Syncfusion OCR Web API converts scanned or image-based PDF documents into fully searchable and selectable text PDFs. It allows you to submit one or multiple PDF files, configure OCR processing options, and retrieve the output through a job-based processing system. The OCR Web API supports multiple languages and includes image-processing enhancements such as grayscale optimization, contrast adjustment, deskewing, denoising, and binarization—to improve text-recognition accuracy through the OCR settings.

Convert Scanned PDFs to Searchable PDF

To convert scanned PDFs into searchable PDFs, send a POST request to the /v1/edit-pdf/ocr endpoint with the input PDF files and OCR settings.

curl --location 'http://localhost:8003/v1/edit-pdf/ocr' \
--form 'file1=@Input1.pdf' \
--form 'file2=@Input2.pdf' \
--form 'settings="{\
  \"Files\": [\
    { \"File\": \"file1\" },\
    { \"File\": \"file2\" }\
  ],\
  \"Language\": \"eng+ara+ell\",\
  \"isToEnhanceGrayscale\": true,\
  \"isToEnhanceContrast\": true,\
  \"isToDeskew\": true,\
  \"isToDenoise\": true,\
  \"isToBinarize\": true\
}"'
const formdata = new FormData();
formdata.append("file1", fileInput.files[0], "Input1.pdf");
formdata.append("file2", fileInput.files[1], "Input2.pdf");
formdata.append(
  "settings",
  JSON.stringify({
    Files: [
      { File: "file1" },
      { File: "file2" }
    ],
    Language: "eng+ara+ell",
    isToEnhanceGrayscale: true,
    isToEnhanceContrast: true,
    isToDeskew: true,
    isToDenoise: true,
    isToBinarize: true
  })
);

const requestOptions = {
  method: "POST",
  body: formdata,
  redirect: "follow"
};

fetch("http://localhost:8003/v1/edit-pdf/ocr", requestOptions)
  .then((response) => response.text())
  .then((result) => console.log(result))
  .catch((error) => console.error(error));
var client = new HttpClient();
var request = new HttpRequestMessage(HttpMethod.Post, "http://localhost:8003/v1/edit-pdf/ocr");
var content = new MultipartFormDataContent();
content.Add(new StreamContent(File.OpenRead("Input1.pdf")), "file1", "Input1.pdf");
content.Add(new StreamContent(File.OpenRead("Input2.pdf")), "file2", "Input2.pdf");
var settings = new
{
    Files = new[]
    {
        new { File = "file1" },
        new { File = "file2" }
    },
    Language = "eng+ara+ell",
    isToEnhanceGrayscale = true,
    isToEnhanceContrast = true,
    isToDeskew = true,
    isToDenoise = true,
    isToBinarize = true,
    Password = (string?)null,
};

var json = JsonSerializer.Serialize(settings);
var settingsContent = new StringContent(json, Encoding.UTF8, "application/json");
content.Add(settingsContent, "settings");
request.Content = content;

using var response = await client.SendAsync(request);
response.EnsureSuccessStatusCode();
Console.WriteLine(await response.Content.ReadAsStringAsync());

OCR Settings

Language

Specifies one or more OCR recognition languages for accurate text extraction. The OCR Web API supports a predefined set of languages, each identified by a language code. To improve recognition accuracy, specify only the languages that are present in the document.

Multiple languages can be provided by combining their codes using the + (plus) separator.

Supported languages:

Code Language
ara Arabic
aze Azerbaijani
bul Bulgarian
cat Catalan
ces Czech
chi_sim Chinese (Simplified)
chi_tra Chinese (Traditional)
chr Cherokee
dan Danish
deu German
ell Greek
eng English
enm Middle English
epo Esperanto
est Estonian
fin Finnish
fra French
frm Middle French
glg Galician
heb Hebrew
hin Hindi
hrv Croatian
hun Hungarian
ind Indonesian
ita Italian
jpn Japanese
kor Korean
lav Latvian
lit Lithuanian
nld Dutch
nor Norwegian
pol Polish
por Portuguese
ron Romanian
rus Russian
slk Slovak
slv Slovenian
sqi Albanian
spa Spanish
srp Serbian
swe Swedish
tam Tamil
tel Telugu
tha Thai
tur Turkish
ukr Ukrainian
vie Vietnamese
osd Orientation and Script Detection

isToEnhanceGrayscale

Converts the image to grayscale to reduce color noise and improve clarity.

isToEnhanceContrast

Increases the contrast between text and background for better recognition accuracy.

isToDeskew

Automatically detects and corrects tilted or rotated pages to ensure proper text alignment during OCR.

isToDenoise

Removes visual noise and artifacts from the image to provide cleaner input for more reliable character recognition.

isToBinarize

Converts the image to high contrast black-and-white to isolate text from the background and improve OCR performance.

OCR PDF Job Response

When the OCR request is submitted, the API creates a background job and returns the job details:

{
  "jobID": "d69b0ef2-b816-4e3b-bc94-1fb35cdfa5bb",
  "status": "requested",
  "createdAt": "2026-03-17T10:11:20Z"
}

Check OCR PDF Job Status

Use the /v1/edit-pdf/status/{jobID} endpoint to check the job progress or download the final processed PDF.

curl --location 'http://localhost:8003/v1/edit-pdf/status/f58c9739-622e-41d4-9dd2-57a901dc13c3' \
  --output Output.pdf
const requestOptions = {
  method: "GET",
  redirect: "follow"
};

fetch("http://localhost:8003/v1/edit-pdf/status/4413bbb5-6b26-4c07-9af2-c26cd2c42fe3", requestOptions)
  .then((response) => response.text())
  .then((result) => console.log(result))
  .catch((error) => console.error(error));
var client = new HttpClient();
var request = new HttpRequestMessage(HttpMethod.Get, "http://localhost:8003/v1/edit-pdf/status/ef0766ab-bc74-456c-8143-782e730a89df");
var response = await client.SendAsync(request);
response.EnsureSuccessStatusCode();
Console.WriteLine(await response.Content.ReadAsStringAsync());

You will receive one of the following statuses until the job is completed. Upon completion, you will receive the actual output file.

Job Statuses:

  • Queued:
{
  "jobID": "4b2782b2-9f08-478b-98fc-4464bd219ca0",
  "status": "queued"
}
  • In Progress:
{
  "jobID": "ef0766ab-bc74-456c-8143-782e730a89df",
  "status": "in progress"
}
  • Error:
{
  "jobID": "ef0766ab-bc74-456c-8143-782e730a89df",
  "status": "error",
  "code": "500",
  "message": "Failed to process OCR"
}

NOTE

The Syncfusion Document Processing API is available as a Docker-based solution. Try it out