How to Compare Scanned PDFs: OCR, Visual Comparison & Best Practices

Scanned PDFs can be harder to compare than regular digital PDFs because their pages may contain images instead of selectable text. This can make it difficult to identify changes in contracts, agreements, invoices, legal records and other documents.

If a scanned PDF does not contain a searchable text layer, a standard text-based comparison may not work effectively. OCR (Optical Character Recognition) can convert text from scanned pages into machine-readable content, while visual comparison can help identify changes that text extraction may miss.

In this guide, you'll learn how to compare scanned PDFs using OCR and visual comparison, when to use each method and the best practices for getting reliable results.

Quick Answer

The best way to compare scanned PDFs depends on what you need to identify. If the PDFs are image-based, use OCR to make the text searchable before comparing the documents. If signatures, stamps, images, formatting, or handwritten notes are important, add a visual comparison step.

For important documents, combining OCR-based text comparison with visual verification provides a more complete way to identify both textual and visual changes.

What Is a Scanned PDF?

A scanned PDF is usually created by scanning a physical document and saving the resulting pages as a PDF. Instead of containing digitally generated text, the pages may consist primarily of images.

For example, a scanned contract may look like a normal PDF when opened, but you may not be able to select individual words or search for specific terms.

PDFs can generally be divided into three categories:

• Digital PDF: Contains machine-readable text that can usually be selected and searched.

• Scanned PDF: Contains page images and may not have a searchable text layer.

• OCR-processed PDF: Contains recognized text created from scanned images.

This distinction matters because text-based comparison requires machine-readable content. If a PDF contains only page images, OCR may be needed before comparing the wording.

How to Tell If a PDF Is Scanned

Before comparing two PDFs, check whether they contain searchable text.

Try Selecting Text

Open the PDF and try selecting a sentence with your cursor. If you cannot select individual words or sentences, the document may be image-based.

Search for a Word

Use the PDF's search function to find a word that is clearly visible on the page. If the search cannot find it, the document may not contain a usable text layer.