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Resize All PDF Pages to A4 converts an entire document to the A4 format, 210 by 297 mm or 595 by 842 points, regardless of what size the pages started at. It is the step that makes a file printable on European and most international office printers, acceptable to submission portals that require A4, and consistent to read on screen. Upload the PDF and the tool first reports what it found, so you know whether the whole file needs converting or only a handful of pages. Choose A4 and decide how the content should behave: Fit to size scales each page proportionally so it fills the A4 frame, which is the right choice when pages came from Letter, A5 or an odd scanned size and should end up looking uniform. Add white space keeps the content at its printed scale and centres it on the A4 page, which matters for forms, drawings and anything where physical dimensions carry meaning; pages larger than A4 are still reduced so that nothing is lost off the edge. Landscape pages can be given A4 landscape rather than being squeezed into portrait, so charts and wide tables remain legible. The conversion runs entirely in the browser with pdf-lib, so the document is never uploaded. For the opposite need, trimming margins rather than changing the page format, use PDF Crop & Resize, and to combine several files before converting them in one pass use PDF Merger.
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.