Before You Compare Two PDFs: A Clean-Diff Checklist
A comparison report is evidence, and evidence is only useful if the two files were comparable in the first place. These are the checks worth making before you run the diff, not after you have quoted it to someone.
Why this comes up
Revised documents arrive from different authors, different machines and sometimes different scanners, so the two files rarely start on equal terms. A missing text layer or a swapped upload order turns a clean report into a misleading one.
Check before you run it
- Confirm both files carry selectable text. The comparison reads the text layer, not the picture of the page. If either file is a scan, run OCR on it first and compare the searchable copy.
- Load the original before the revision. The tool compares exactly two files, and the order tells the report which side is which. Renaming the files first makes the later download easier to file.
- Agree what counts as a change. A reissued layout with new page numbers produces plenty of movement; start with the key changes for figures and dates, then read the page-level detail in context.
When to reach for it
- A tender response was resubmitted with revised pricing. You need the figures and dates that moved, not a general impression that the document looks different.
- Two teams edited separate copies of the same policy. Compare them before choosing a master copy so nothing agreed in either version disappears.
One question we get
Can I run Compare from the API?
Yes — POST /v1/compare-pdf is live and costs 5 credits. Send file_a and file_b with a bearer key; the JSON contains stats, changed blocks and key differences. See the API page.
Where it fits
The tools people usually open next to Compare PDF:
- Flip — Mirror PDF pages horizontally or vertically.
- Split in half — Split two page layout scans, A3 to double A4 or A4 to double A5.
- N-up — Print multiple pages per sheet per paper.
Every tool works on a copy, so the original file is never touched. Uploads are stored under an unguessable id and deleted automatically two hours after you last open them; nothing is listed, shared or indexed. More on the security page.