Free online PDF comparison tool — highlight text differences line by line, pure frontend processing
The tool uses pdf.js to extract text from both PDF files in your browser, then applies the LCS (Longest Common Subsequence) algorithm to compare them line by line. Added lines are highlighted in green, removed lines in red, and unchanged lines have no highlight. All processing happens locally — your files never leave your device.
This tool extracts the text layer from PDFs for comparison. Scanned PDFs that are images without a text layer cannot be compared. We recommend using an OCR tool first to convert scanned PDFs to searchable PDFs.
Green background indicates added lines (present in the modified PDF but not in the original), red background indicates removed lines (present in the original but not in the modified), and no background means unchanged lines.
The tool uses pdf.js to extract text from both PDFs in your browser, then applies the LCS algorithm to compare line by line. Added=green, removed=red, unchanged=default. All processing is local.
This tool extracts the text layer. Scanned image PDFs without text layer cannot be compared. Use OCR first.
Green=added lines, red=removed lines, no background=unchanged lines.