How to compare PDF files
- Choose Compare PDF files free and use Attach Two PDFs. Select both versions together, or attach them one at a time, checking the filenames shown in the workspace.
- Choose Compare PDFs to begin. Wait for the comparison to finish; long documents and image-heavy pages can require more processing time and browser memory.
- Read the results for each corresponding page. The tool can flag text changes, visual changes, changed page sizes or a missing page in one file.
- Inspect the side-by-side previews around each flagged area. Confirm the meaning of the difference against your source documents before approving, signing or circulating the revision.
When comparing PDFs helps
An updated quotation may look familiar while a quantity, unit price or delivery date has changed. A new brochure could use the same wording with a different photograph. A revised meeting pack may add a page or alter a table. Reviewing versions together helps you decide which sections deserve closer attention instead of repeatedly switching between separate viewer windows.
For a practical review, choose files from the same document lineage and verify which one is the newer version. Use clear filenames, and keep the originals available. A flag tells you that something may differ; it does not tell you whether the change is authorized, accurate or acceptable.
Understand what the comparison measures
FlowPDF compares page 1 with page 1, page 2 with page 2, and so on. Text checks use words extracted from the PDF; visual checks use rendered page pixels. A scan may have no extractable text but still produce a visual difference. Font substitution, rendering variations or image quality can also affect results, so investigate the document rather than treating every flag as an editorial change.
What this comparison does not do
The tool does not automatically align sections after an inserted page. If one version adds a cover, subsequent page pairs may no longer represent the same material. It is not a word-processing tracked-changes system, a semantic contract review, or a forensic inspection of hidden metadata. A match is not proof that the underlying files are byte-for-byte identical. Tiny differences or unusual PDF features may need a separate manual check, especially for high-stakes documents.
Keep document review local
Both PDFs are processed in the browser and are not uploaded to a FlowPDF server. You can compare them without opening an account. The website still loads resources and may collect limited website analytics, as explained in the privacy policy. Keep confidential originals and your review decisions in an appropriate location on your own device.