Compare Two PDFs

About comparing two PDFs

Someone sends back "the updated contract". It looks the same. It is forty pages long. Somewhere in it, something moved.

That is the whole problem. You know a document changed, you do not know *where*, and reading both copies side by side is how people lose an afternoon and still miss the one clause that mattered.

This tool reads the text out of both PDFs and shows you only what is different — the changed lines highlighted down to the individual words, the added lines in green, the removed ones in red.

What you get

The result is a side-by-side table. The original is on the left, the new version on the right, with line numbers down both sides:

• Changed lines appear on both sides, with the exact words that differ marked inside the line
• Added lines appear only on the right
• Removed lines appear only on the left
• Unchanged lines stay in place, so you always know where you are in the document

At the top you get the count: how many lines changed, how many were added, how many were removed. If nothing moved, it tells you that plainly instead of leaving you to scroll and hope.

The options, and when to change them

• Ignore spacing (on) — treats "1 January" and "1 January" as the same. Leave it on. Two PDFs made by different tools disagree about spaces constantly, and every one of those would otherwise be reported as a change you do not care about.
• Ignore upper/lower case (off) — turn it on when a rename or a style change has swept through and you only want real edits.
• Ignore blank lines (on) — page breaks and spacing rarely matter. Turn it off if the layout itself is the thing being checked.
• Join wrapped lines into paragraphs (on) — a PDF breaks a sentence wherever the page ran out of width. With this on, a whole paragraph is compared as one unit, so adding a single word early on does not report every line after it as changed. Turn it off for tables, price lists and anything where the line is the meaning.

It compares the text, not the picture

The comparison is on the words the PDF actually stores, so it is exact and instant — a 200-page document takes a couple of seconds.

What it does not do is compare the *appearance*. A change of font, a moved logo, a different margin or a new colour will not show up, because none of that changes the text. If the layout is what you need to check, turn both files into images with PDF to JPG and look at the pages.

A scanned PDF cannot be compared at all. A scan is a photograph of a page with no text inside it. Reporting "identical" about two scans would be worse than reporting nothing, so the tool stops and says so instead.

Neither file is uploaded

Both PDFs are opened and read inside your browser, on your device. Nothing is sent to a server, nothing is queued, nothing is stored.

This is the whole reason a tool like this belongs in the browser. The documents people need to compare are contracts, tenders, statements, policies, court filings and drafts under NDA — exactly the files you should not be dropping onto a stranger's server to save ten minutes.

What people use it for

• Checking what a counterparty changed in a returned contract
• Comparing draft and final versions of a report or a policy
• Finding the edit between v2 and v3 when nobody kept a changelog
• Checking a quote or invoice against the one you agreed
• Seeing what moved in a new edition of a manual, a standard or a syllabus
• Confirming that a re-exported PDF really is identical to the old one

Good to know

• A password-protected PDF must be unlocked first — use Unlock PDF
• Both files are compared in full; to compare only part of them, pull the pages out with Split PDF first
• The Download the changes button saves a plain-text summary of just the differences — useful to paste into an email or keep with the file
• Very long documents can exceed what a browser can diff in one pass; the tool will say so and point you at doing it a page range at a time
• Columns, tables and footnotes come out in the order the PDF stores them, which is usually — but not always — the reading order
• This uses the same engine as Text Diff; that page is the one to use when you already have the text

How to use it

• Upload the original PDF on the left and the changed one on the right
• Leave the options as they are for a normal document
• Press Compare
• Read the highlighted differences, and Download the changes if you need a summary to send

Related tools

• Text Diff — the same comparison, for text you already have
• PDF to Text — pull the text out of one PDF to keep or edit
• Compare Excel Files — the spreadsheet equivalent, cell by cell
• Compare Two Folders — which files differ, across whole folders
• PDF to JPG — compare how the pages *look*, not what they say
• Unlock PDF — remove a password before comparing