Resize PDF to A3 converts every page of a document to A3, 297 by 420 mm, which a PDF stores as 841.89 by 1190.55 points. A3 is exactly twice the area of A4, and because every A size shares the same proportions, an A4 page enlarged to A3 fills it perfectly at 141% with no white bands and nothing cropped. That makes the conversion the standard step for printing posters, floor plans, technical drawings, school projects and presentation boards on A3 paper, or for sending a file to a print shop that asks for the final format rather than an A4 file to be scaled at the counter. Choose Fit to size to enlarge smaller pages so they fill the sheet. Add white space does the opposite: it keeps content at its original printed scale and centres it, which is useful when a drawing is to scale and must not be enlarged, for example placing an A4 plan on an A3 sheet with room for notes. Landscape pages can become A3 landscape, 420 by 297 mm, the usual orientation for plans and charts. Vector content such as text, lines and CAD exports stays perfectly sharp after enlarging. Scanned pages and photos are images, so enlarging them by 141% spreads the same pixels over a bigger sheet: a 300 dpi A4 scan prints at about 212 dpi on A3, which is still fine for most uses. The PDF is processed in your browser and never uploaded. To reduce an A3 file for office printing use Resize All PDF Pages to A4, and to trim the margins first use PDF Crop & Resize.
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.