How does the tool catch changes to signatures or images that have no text?

Alongside the text comparator, the Visual Pixel Diff engine renders each page of Document A and Document B onto hidden HTML5 canvases and compares the RGB color values of every single pixel. Any added signature, altered chart, or moved logo lights up in bright crimson.

What happens if someone adds a sentence at the top of a page and pushes the rest of the text down?

In Visual Pixel Diff mode, the downward shift will highlight the moved paragraphs because their vertical coordinates changed. Switching to the Line Text Diff tab ignores vertical pixel coordinates and isolates only the exact sentence that was added or deleted.

Can I compare two PDFs that have different total page counts?

Yes. The inspector compares all pages up to the length of the longer document. Any extra pages added at the end of Document B (or removed compared to Document A) are automatically flagged with a change indicator dot.

What is included in the downloadable Diff Audit Report PDF?

Clicking Download Diff Audit Report generates a standalone PDF summary listing both filenames, the timestamp, total pages compared, how many pages had differences, the pixel delta percentage per page, and the exact added/removed text lines.

Are my two contracts uploaded to a cloud server to run the comparison?

Never. Both PDF files stay in your local browser memory. All text extraction, canvas pixel diffing, and audit report generation run 100% on your device.

Can I compare password-protected PDF files?

Yes. If either Document A or Document B is locked with an open password, an inline password prompt lets you unlock it in browser memory before the comparison runs.

Compare Two PDF Files Online: Visual & Text Diff Tool

When a client or counterparty returns a "signed" 20-page PDF contract, how do you know for sure they did not quietly change a payment term on page 9 or swap a diagram on page 14? Drop both versions here to compare two PDF files directly in your browser. The workspace runs two comparison engines in parallel: a Line-by-Line Text Diff that flags added and deleted wording, and a Canvas Pixel Diff that highlights moved signatures, logos, or layout shifts in crimson.

Why you need both text comparison and pixel comparison for PDFs

Comparing two PDF revisions is harder than comparing two plain-text code files because a PDF can change in two completely different ways.

First, someone can edit a word or a number - changing a net payment term from 30 days to 60 days, or deleting an indemnity sentence. A Text Diff engine extracts the text lines from Page N of Document A and Page N of Document B, stripping out noise so you can read the exact deleted line in red (-) and the added replacement line in green (+).

Second, someone can alter something that has no text characters at all: adding a wet-ink signature image, changing a number inside a flattened chart bitmap, moving a table border, or replacing a company seal. A text-only comparator would report "100% identical" even if a diagram was completely swapped! Running a Visual Pixel Diff renders Page N of both PDFs onto matching HTML5 canvases and compares every (R, G, B) pixel pair, lighting up any visual discrepancy in bright crimson.

How to compare two PDF files step by step

Drop your original Baseline PDF (Document A) into the upload zone, or click Load Sample PDF to test immediately with two built-in contract revisions.
Click Select Revised PDF (Document B) in the left sidebar (or center prompt) to load the second file you want to compare against Document A.
Look at the Page Selector Pills (P.1 ●, P.2, P.3 ●): any page with a dot badge (●) has detected differences between Document A and Document B.
Switch between Side-by-Side View, Visual Pixel Diff, and Line Text Diff tabs to inspect every change, or click Download Diff Audit Report (.PDF) to export a permanent summary.

Three inspection views plus a downloadable PDF audit report

Instead of making you squint at two separate browser windows, the comparison inspector links both documents page-for-page inside a unified stage.

Page-by-page change indicator pills: Automatically scans all pages across Document A and Document B as soon as both files load, badging every modified page with a dot (●) and reporting the total number of changed pages in the sidebar.
Visual Pixel Diff heatmap canvas: Renders Page N of Document A and Page N of Document B at matching dimensions, computes the per-pixel RGB distance across the entire page bitmap, draws unchanged regions as a faded ghost background, and highlights changed pixels in high-contrast crimson (#dc2626) with an exact pixel delta percentage readout.
Line-by-Line Text Diff view: Compares normalized text lines on each page, displaying removed lines from Document A in red (- ...) and added lines in Document B in green (+ ...).
Synchronized Side-by-Side canvas view: Shows Baseline A on the left and Revised B on the right at identical scale for human visual verification.
Exportable PDF Diff Audit Report: Generates a clean, standalone PDF report listing the compared filenames, total pages, modified page count, pixel delta percentages, and the exact added/removed text lines for every changed page.

Worked example: auditing a 14-page NDA returned by a vendor

Suppose you sent Mutual-NDA-Draft-v1.pdf (14 pages, 640 KB) to a prospective vendor, and they return Mutual-NDA-Signed-v2.pdf (14 pages, 655 KB) saying "Signed with no changes."

You load v1 as Document A and v2 as Document B:

Within 0.9 seconds, the sidebar summary reports: 2 of 14 pages contain differences (Pages 6 and 14). Pages 1–5 and 7–13 show zero text or pixel changes.
You click the P.6 ● pill and switch to Line Text Diff:

Red removed line: - 4.2 Confidentiality obligations shall remain in force for five (5) years.
Green added line: + 4.2 Confidentiality obligations shall remain in force for two (2) years.

You click the P.14 ● pill and switch to Visual Pixel Diff: the text diff says no printed words changed on Page 14, but the Pixel Diff canvas highlights a 1.84% pixel delta in crimson right on the signature block where the vendor placed their scanned PNG signature image.
You click Download Diff Audit Report to save a 2-page PDF summary documenting the unauthorized edit on Page 6 before replying to the vendor.

Tips for comparing scanned PDFs and reflowed documents

When comparing two digital PDFs exported from the same word processor, both the Text Diff and the Visual Pixel Diff pinpoint single-word edits with surgical accuracy.

If someone adds a three-line paragraph at the very top of Page 2, every subsequent line on Page 2 shifts downward by half an inch. On the Visual Pixel Diff tab, that vertical shift will highlight all the shifted paragraphs below it because their pixel coordinates moved; switching to the Line Text Diff tab immediately isolates just the three newly inserted lines of text without getting distracted by the vertical layout shift.

Conversely, if you are comparing two flatbed scans of paper documents, slight paper alignment shifts will light up the Pixel Diff across the page edges, so check the Text Diff tab (if OCR is present) or Side-by-Side view.

Confidentiality and local browser execution

Contracts, M&A term sheets, patent drafts, and engineering blueprints are among the most confidential files you handle. Both Document A and Document B are parsed, rendered, and compared 100% locally inside your browser tab using PDF.js, HTML5 Canvas, and pdf-lib. Zero bytes leave your device.

Related comparison and PDF tools

If you want to compare raw source code, JSON payloads, or pasted plain-text paragraphs with character-level highlighting, open the Code & Text Diff Checker. You can also extract raw text from a single PDF in PDF to Text & Markdown, black out disputed clauses in PDF Redactor, or sign the verified contract in PDF Signer & Validator.

PDF Compare & Visual Diff