How to compare two versions of a PDF

Why compare visually

• It catches every kind of change: A visual comparison looks at what each page shows, so it catches every kind of change: a new word, a different number, a swapped logo, a moved signature line or a changed table border. It works the same for text, drawings and scans.
• Text-only comparison misses things: Comparing only the text would miss changes to images and layout, and would be thrown off by line breaks.
• What Compare PDF does: Compare PDF does both: it boxes every area where the pages look different, and it also reads the text blocks so it can tell you what was added, removed or moved.

Getting the files ready

• Original first, revision second: Add the original first and the revised version second, so the labels in the viewer and report are the right way round.
• Use the real files instead of printouts scanned back in, because two scans of the same paper never line up exactly and show small false changes.
• Remove pages the other doesn't have: If one file has a cover page or a signature page the other doesn't, remove it first with Extract Pages so the page numbers line up.
• Pages match by position: Pages are compared by position, page 3 against page 3.

Reading the three views

• Side by side is the best place to start. The columns scroll together and red boxes show where each page differs.
• Overlay stacks the revised page on the original with a slider, so moving it back and forth makes shifted lines and changed words jump out.
• Difference view blends the two so everything identical turns black; only changes stay visible, which is handy on busy pages like spreadsheets and plans.
• Skip unchanged pages: Tick "only pages with changes" on long documents to skip everything that's the same.

Making sense of added, removed and moved

• The per-page list: Below the viewer, each changed page lists its added, removed and moved text blocks.
• An edit shows as removed plus added: A removed block next to an added block with nearly the same words usually means one sentence was edited, so read both carefully.
• A moved block means the same content is now in a different spot, which often happens when a line was added above it.
• A run of moved blocks: If many pages in a row show only moved blocks, something near the start of that run pushed the content down, and the real change is on the first page of the run.

When every page looks different

• An early insertion shifts everything: If a paragraph was added early in the document, everything after it shifts, and page by page comparison shows changes everywhere.
• Find where it starts: Find the first page where the differences start; that's where the insertion is. Then compare the remaining sections separately by extracting matching page ranges from each file.
• When reformatting defeats it: For documents that were fully reformatted, a visual comparison isn't the right tool. Ask the AI PDF Workspace to compare the two versions clause by clause instead, and check its page references.

Keeping a record

• Download the report: Download the PDF report when you need to show someone what changed or keep proof of your review.
• What it contains: It starts with a summary of both files and the number of changed pages, then shows each changed page side by side with the differences outlined and a short list of added and removed text.
• Lock the final version: Once everyone agrees on the final version, lock it with Flatten PDF or protect it, so nothing changes after the review.

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