How does this PDF comparison tool work?

This tool extracts text from both PDF files using pdf.js, performs a difference analysis, and highlights added, removed, and modified content. Everything runs locally in your browser.

Does this tool upload my documents?

No. Both PDFs are processed inside your browser. Nothing is sent or stored externally.

Can I compare scanned PDFs?

Text comparison works only if the PDF contains selectable text. For scanned images, OCR must be applied first using a separate OCR tool.

Can I download the difference report?

Yes. The tool generates a comparison report that can be downloaded as a text file or ZIP file.

Compare PDFs Online — Highlight Differences Between Two PDF Documents

Upload two PDFs and instantly detect differences — added text, removed text, modified sentences, and structural changes. Fully private, browser-based, and fast.

Compare Two PDF Files

Select First PDF Select Second PDF

How This PDF Comparison Tool Works

Comparing two PDF documents is one of the most essential tasks for researchers, students, lawyers, editors, companies, auditors, government officers, and anyone working with multiple versions of contracts or academic files. This tool enables you to identify every difference between two PDFs instantly — without uploading anything to a server.

Why PDF comparison matters today

In professional environments, PDF documents are the standard format for contracts, agreements, academic submissions, policies, manuals, and research manuscripts. With frequent revisions, it's critical to understand what has changed between:

Version 1 and Version 2 of a contract
Two drafts of a research paper
Updated policy documents
Multiple revisions of legal filings
Different versions of government forms
Company reports before and after edits

Text Extraction Engine

This tool uses pdf.js to extract all text from each page of the PDF. PDFs store content in complex structures, but pdf.js allows reading:

Plain text
Ordered sequences of characters
Page-level structure
Unicode content

Page-by-page extraction

Each PDF is read into memory, and text from each page is extracted separately. After extraction, the text is normalized:

Converted to consistent spacing
Whitespace simplified
Hidden formatting ignored
Broken words reconstructed

Difference Detection (Diff Engine)

The heart of this tool is the difference engine powered by diff.js. It analyzes two text blocks and identifies:

Added text (highlighted in green)
Removed text (highlighted in red with strike-through)
Modified content (highlighted in yellow)

This type of analysis is extremely accurate for any PDF that contains selectable text. If a PDF is scanned, you must apply OCR first.

Use cases of PDF comparison

1. Legal & Contract Analysis

Law firms frequently receive multiple versions of agreements. Even small changes can have major legal impacts. This tool makes it easy to see:

New clauses added
Deleted clauses
Modified sentence structures
Changed numbers or dates

2. Academic & Research Workflow

Researchers work with evolving manuscripts. Differences can include:

Updated methodology
Corrected formulas
Added citations
Rewritten abstract

3. Business Documentation

Companies update:

Policies
Reports
Financial statements
Employee contracts

4. Government & Public Administration

Forms and guidelines are often updated yearly. This tool highlights policy changes instantly.

5. Editing & Publishing

Editors compare:

Original vs final versions
Content revisions
Typographical corrections

Advantages of Browser-Based Comparison

Unlike cloud-based comparison tools:

No data leaves your device
No upload delays
No document storage
No risk of unauthorized access
Suitable for confidential documents

How differences are displayed

The output uses color-coded marking:

Green background = Added text
Red background = Removed text
Yellow background = Modified content

Every difference is visible instantly and can be copied or downloaded as a report.

Report Generation

Users can download:

A plain text difference report
A ZIP file with page-by-page differences

Limitations

Scanned PDFs require OCR first
Complex layouts (tables, diagrams) are compared as text only
Fonts and styles are not compared

Conclusion

This PDF comparison tool is built for professionals, students, lawyers, editors, and anyone handling important documents. It offers a privacy-first, browser-only approach that ensures your files remain secure while providing a deep and accurate comparison of textual differences.

Tips & Troubleshooting

Comparison is most reliable when both PDFs are the same kind of document (two versions of the same report, contract, or form).

Best practices

Compare final exported PDFs rather than drafts from editors; you’ll get more stable, predictable results.
If one file is scanned and the other is selectable text, differences may be less meaningful—try to compare like-for-like.
After comparison, manually verify any highlighted changes (especially in legal or financial files).
Use versioned filenames (v1, v2, final) so you never mix the inputs.

If something goes wrong

If no differences show, the PDFs may be text-identical (or changes are layout-only). Zoom in to check formatting shifts.
If you see errors, re-save both PDFs from a trusted viewer and retry.
If documents are very large, extract the relevant pages first and compare only that subset.

Privacy note

Both inputs are processed in the browser session. No server upload is required to generate the comparison output.

Useful next steps

Extract pages — Compare only the pages that matter to speed things up.
PDF Tools hub — Redact sensitive info or sign the final version.
Checklist before sending — Avoid sending the wrong version.