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A PDF with pages of different sizes usually comes from one of four places: a scanner that cropped pages slightly differently, a document where an A3 spread or a landscape chart was inserted into an otherwise A4 file, a merge of sources created in regions that use A4 and Letter, or a page that was replaced later from another document. The file looks correct on screen, so the mismatch is discovered only when printing, uploading or binding goes wrong. This tool starts by measuring every page and telling you what it found, including the exact page numbers in each size group, so you can see at a glance whether three pages are the problem or thirty. From there one button sets every page to the size the majority already use, or you can choose A4, Letter, the largest page, or a custom size. Content can be scaled to fill the new page or left at its original scale with white space added around it, and landscape pages can keep their orientation so wide content stays readable. Nothing is uploaded; the measurement and the rewrite both happen in your browser. To trim uneven margins instead of changing page dimensions, use PDF Crop & Resize, and to check the finished document use PDF Page Count Checker.
The reason inconsistent page sizes are so annoying is that nothing warns you about them. A PDF viewer happily renders a file where page 4 is Letter and the rest are A4, and the difference is only 6 mm wider and 13 mm shorter, which is invisible on screen. The cost arrives at the end of the process: a print driver set to "actual size" produces pages with different margins, a duplex job feeds wrongly, a submission portal that validates page dimensions rejects the upload, or a reader sees the page jump as it scrolls. Most PDF services offer resize, crop and compress as separate operations and leave the diagnosis to the user, which is the hard part. This tool inverts that order. It measures first, tells you in plain language what it found, and offers one button that applies the obvious fix. Only if you want something else do the other options matter. A few practical notes. Scanned pages rarely match a standard format to the decimal, so sizes within roughly 0.7 mm of each other are treated as the same format rather than reported as separate groups; this keeps the summary honest instead of listing twenty near-identical sizes. Pages carrying a rotation flag are measured as the reader sees them, so a portrait page rotated 90 degrees is correctly grouped with the landscape pages. The output is a standard PDF that opens in Acrobat, Preview, Chrome and any mobile reader, with text, fonts, links and images preserved. If your real problem is uneven white margins rather than uneven page sizes, PDF Crop & Resize is the better tool, since it trims the margins directly. If pages came from several source files, run PDF Merger first and normalise the combined document in one pass, and use PDF Page Count Checker to confirm the final file has every page you expect.