The other side sends back a “revised” agreement, and the covering email says only that it contains some minor changes. Reading both copies side by side takes an hour and still leaves you wondering whether you missed a number. A comparison does that part in seconds, and shows you exactly where to look. This guide is about using one well, and about what it cannot tell you.
Why reading both is risky
People are poor at spotting small differences in text they already know. The eye fills in what it expects to see. The changes that matter most in a contract tend to be the ones that are easy to miss: a number that moved from 30 to 45, a “may” that became “must”, a clause that quietly disappeared, a schedule that was swapped for an older one.
A comparison does not get tired and does not expect anything. It lines the two documents up word by word and lists every difference, so your attention goes to judging the changes instead of hunting for them. Its limit is that it knows nothing about meaning. A change from “shall” to “may” and a change from “colour” to “color” look equally big to it.
Get the two files ready
- Make sure you have the right pair. Name them clearly, such as agreement-v1-sent.pdf and agreement-v2-returned.pdf. Putting the older one first is what makes “added” and “removed” mean what you expect.
- Check each file has real text. Click and drag over a sentence in a reader. If you can select words, there is a text layer. If you cannot, it is a scan, and you should run OCR PDF first.
- Flatten forms and comments if they matter. The comparison reads the text printed on the pages. Values typed into form fields and review comments are better fixed into the page first with Flatten PDF.
- Keep the originals. Work on copies, so you can show later exactly what you compared.
Run the comparison
Open Compare PDFs, add the older file on the left and the newer one on the right, and press Compare. For short documents the option to also compare how the pages look is ticked for you. It draws both files and marks places where the pictures differ, which catches a changed logo, a new stamp or a different table border that no word list would show. It takes roughly one to four seconds per page, so for a long document you may prefer to leave it off at first.
Nothing is uploaded. Both files stay on your device, which is the right way to handle a draft agreement that has not been signed yet.
Reading the list: what to check first
The result shows every change in a list, with old words struck through and new words beside them. Click one to see it in both files. Work through them in this order, not top to bottom:
- Numbers, dates and periods. Prices, fees, interest rates, percentages, notice periods and deadlines. These are the changes with the most direct effect and the easiest to hide in a long sentence.
- Removed text. Red entries are wording that is gone. Ask why each one was taken out, and whether anything elsewhere now depends on it.
- Small word changes with big effects. “May” and “must”, “and” and “or”, “reasonable” and “absolute”, “including” and “limited to”.
- Defined terms and names. A change to a party’s name, an address or a defined term can ripple through the rest of the document.
- Added text. Green entries are new wording. Read each one in its paragraph, not only in the list.
- Everything else, such as moved paragraphs, which appear once as removed and once as added, and harmless typographic changes.
A worked example
Take a two-page services agreement. You sent a first version and the other side returned a revision. Compared, the list shows these among its changes: the delivery period changed from 14 to 21 days, the payment term from 30 to 45 days, and a setup fee on the schedule from 1,800 to 2,400 pounds. A clause allowing the supplier to use subcontractors without the customer’s consent was replaced by one about confidentiality.
Notice what the order of reading does. Three of the changes are single numbers that a quick read could pass over, and together they shift money and time in the other side’s favour. The reworded clause is the one a person would notice, and the numbers are the ones the list rescues. With the look check on, the comparison also marks a new coloured box on page 2 that has no words in it at all, which is worth a glance to see what was added to the page.
Things a text comparison can miss
- Scans. No words, no comparison. The tool names pages without text so that “no changes” is never mistaken for “no differences”.
- Meaning. A sentence can keep the same words but change its effect through its position, for example under a different heading. A moved paragraph shows as removed and added; check where it landed.
- Formatting that carries meaning. Bold, strikethrough and highlighting can mean something in a draft. Font and size changes are not counted as word changes, so use the look check for those.
- Cross-references. A clause number that shifted by one can leave references elsewhere pointing at the wrong clause. The comparison will show the number changes but not that a reference is now wrong.
- Re-typed documents. If the other side retyped the agreement instead of editing it, expect small differences throughout. Read the list for the substantive ones.
- Case and punctuation. A capital letter or a full stop counts as a change. That is deliberate, because in a defined term it can matter.
Keeping a record
The tool offers three downloads. The PDF report and the plain-text report list each change with its pages, which is useful to attach to your notes or to send to an adviser. The copy of the newer file with the differences marked adds highlights and notes you can switch off, which is handy for sending back with questions. Save the report next to the two files so the comparison can be repeated and explained later.
If the document ends up needing a signature, remember that a signed PDF cannot be altered without breaking the signature. Our guide to visual and digital signatures explains what a signature does and does not protect.
A checklist
- Older file on the left, newer on the right?
- Both files have selectable text, or have been through OCR?
- Numbers, dates and periods checked first?
- Every removed passage understood?
- Changed small words read in context?
- Moved paragraphs located in their new place?
- Look-different areas on each page glanced at?
- Report saved with the two files?
- For anything that matters, reviewed by a qualified adviser?
A comparison shows what changed, not what it means. Use it to be sure you have seen every difference, then decide about each one yourself or with a professional.
Frequently asked questions
Is a text comparison enough to be sure a contract has not changed?
It is a strong first check for wording, and the look-different check adds images and layout. It is not a substitute for reading the changed parts in context, and for anything important a qualified adviser should review the document.
What if the other side sent a scan?
A scan is a picture of text, so there are no words to compare. Run OCR first, then compare. Expect a few recognition errors to show up as differences.
Do I need the Word files?
No. You can compare the PDFs directly. If you have both Word files, Word’s own compare feature shows tracked changes, but you may only ever have the PDFs.
Why do small changes appear at line ends?
If the text was re-flowed, a word hyphenated at the end of a line in one version and not in the other reads as a different word. Look past those to the real wording changes.
Are my documents uploaded?
No. Both files are compared in your browser on your own device, which matters for contracts and drafts that must stay confidential.