[Public] Handling Stuck Processes When Loading PDF Forms in Linux with IronOCR

IronOCR is a robust OCR engine for .NET, widely used for reading text from PDFs and images. However, when running on Linux (e.g., Debian with .NET 8), developers may encounter a critical issue: the process can hang indefinitely when loading certain PDF files with interactive forms using OcrInput.LoadPdf().

This article explains the issue and outlines a reliable workaround to ensure stability in production environments.

The Problem

When using the following code to load a PDF with form fields:

The process gets stuck and never proceeds beyond the LoadPdf() call.

What Works

• The same PDF loads correctly on Windows.

• Other PDF files (even with form fields) may not cause issues — making this problem inconsistent and hard to detect upfront.

Workaround: Flatten the PDF Before OCR

To avoid this issue, the recommended workaround is to flatten the PDF with interactive forms before loading it into IronOCR.

Flattening a PDF converts all form fields into regular static content, removing the interactive layer that causes the hang.

How to Flatten the PDF (Example using IronPDF)

If you're using IronPDF, you can flatten the file easily before passing it to IronOCR:

using IronPdf;

var pdf = PdfDocument.FromFile("ocrpdfform.pdf");
pdf.Flatten();
pdf.SaveAs("flattened_ocrpdfform.pdf");

// Now load the flattened version safely
using var ocrInput = new OcrInput();
ocrInput.LoadPdf("flattened_ocrpdfform.pdf); // No longer stuck


//Once flattened, you can proceed with OCR as usual:

 
var ocr = new IronTesseract();
var result = ocr.Read(ocrInput);
Console.WriteLine(result.Text);

Benefits of Flattening

• Prevents hangs during LoadPdf() on Linux

• Ensures consistent behavior across platforms

• Strips unnecessary interactive elements not needed for OCR

• Reduces file complexity, improving processing speed