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Compare PDF Files

Compare PDF files to find what changed between two versions. Added, removed and changed words are highlighted side by side or inline, with page numbers, jump-to-next-change and export — all in your browser.

Original PDF

Changed PDF

How it works

Comparing two PDFs

Open the original and the changed PDF. The text of every page is read on your device with PDF.js.
The text is tidied: extra spaces are collapsed, ligatures like “ﬁ” are spelled out, and words split with a hyphen at a line end are joined.
Each document is split into sentences (or kept as lines), remembering which page each one starts on, and compared with the same engine as Text Compare.
Changed sentences are shown with the exact words highlighted. Use the arrows to jump from change to change, and export a .diff or HTML report.

Reading the result

Red is text only in the original; green is text only in the changed PDF. In changed sentences, the words that differ are marked more strongly.
Page numbers sit beside every row (p3 is page 3), and a divider shows where each side moves to a new page.
Unchanged text is folded away, with a little context around each change. Click to expand it, or tick “Show unchanged text”.
Visual mode shows one page of each side by side, plus a third image with the differing pixels in red.

Limitations, plainly

Scans have no text. If a PDF is a scan or made of images, run it through PDF OCR first, or use Visual mode.
Reading order comes from the PDF. Multi-column pages, tables and text boxes can be read in an odd order, which can show moved text as removed and added.
Formatting isn't compared in text mode — bold, fonts, colors, images and spacing changes don't show. Visual mode catches them on pages with the same layout.
Sentence splitting is a best guess. Abbreviations and unusual punctuation can split or join sentences differently; switch to Lines if that gets in the way.
Password-protected PDFs can't be opened — remove the password with Unlock PDF first. Up to 200 MB and 2,000 pages per file.

Frequently asked questions

Are my PDFs uploaded anywhere?+

No. Both PDFs are opened and compared entirely in your browser — the text is read with PDF.js and compared in a background worker on your device. Nothing is sent anywhere or stored.

Why does it say there's no text in my PDF?+

Scanned documents and PDFs made from photos are pictures of pages — there are no letters in them for a text comparison to read. Make the text searchable first with PDF OCR (tools.northlane.live/pdf-ocr/), then compare the OCR'd copies, or use the Visual mode here, which compares the rendered pages pixel by pixel.

Why doesn't a change in line breaks show as a difference?+

In Sentences mode, the text of each PDF is joined up and split into sentences, ignoring where lines and pages break. That way, an edit that pushes text onto the next line or page doesn't make everything after it look changed. Words hyphenated across a line end (like “docu-ment”) are joined too. Switch to Lines to compare the layout line by line instead — better for tables and forms.

Does it compare formatting, images or layout?+

Text mode compares only the words. Changes in fonts, colors, images, spacing or page layout aren't detected. Visual mode renders a page of each PDF and highlights pixels that differ, which catches those — but a small shift moves everything after it, so it works best for pages with the same layout.

Can I save the comparison?+

Yes. Download a .diff file (the unified format used by developers' tools) or an HTML report with the two versions side by side and changes highlighted, which you can open in any browser and print or save as PDF. You can also copy the diff to the clipboard.

What about password-protected PDFs?+

PDFs that need a password to open can't be read here. Remove the password first with Unlock PDF (tools.northlane.live/unlock-pdf/).

How do I compare two versions of a PDF?+

Open the original and the changed PDF, and the differences are listed straight away — side by side or inline, with added and removed text highlighted by word or by character. A summary names the pages with changes, and unchanged text is folded away until you tick “Show unchanged text”.

Can I ignore differences in capitals or spacing?+

Yes. Tick Ignore case to treat “Total” and “total” as the same, and Ignore all spacing to skip changes that are only extra or missing spaces. If nothing else differs, the result says the text is the same with the selected options.

Can I compare a PDF with a Word document?+

Both files need to be PDFs. Save the Word document as a PDF first (File › Save As › PDF in Word), then compare the two. To compare plain text you've copied from anywhere, Text Compare is quicker.

Can I compare more than two PDFs?+

No — two at a time: an original and a changed version. To check several drafts, compare them in pairs, for example draft 1 with draft 2, then draft 2 with draft 3.

Is there a size or page limit?+

Each PDF can be up to 200 MB and 2,000 pages. Text mode compares the whole documents; Visual mode compares one page of each at a time, which you pick from a list.