Page size and file size are different problems
The most common confusion around "resizing a PDF" is the difference between the size of the file and the size of the pages. File size is measured in megabytes and matters for email limits and uploads - that is what our Compress PDF tool handles. Page size is measured in millimetres or inches and describes the physical sheet the page represents: A4, US Letter, Legal and so on. A 40 MB PDF can have perfectly normal A4 pages, and a 200 KB PDF can have pages the size of a poster. This tool changes page dimensions. If you need both - say, an oversized scanned contract that also needs to squeeze under a 10 MB portal limit - resize it first, then run the result through Compress PDF.
What actually happens when a page is resized
A PDF page carries a MediaBox: two coordinates that define its width and height in points (1 point = 1/72 inch). Resizing rewrites that box and scales the page's content to match. PDFBEAR does this mathematically rather than by re-rendering the page as a picture, which is why the output keeps all the properties of a real document: text remains selectable and searchable, vector graphics stay razor sharp at any size, and clickable links move together with the words they cover. Scanned pages - which are photographs internally - are scaled like photographs: shrinking them is visually lossless, while enlarging them beyond roughly 150% will start to look soft, exactly as enlarging any photo would.
Choosing between a paper size and a percentage
Use a paper size (A4, Letter, Legal, A3, A5) when the destination is known: a printer tray, a binding service, a government upload that validates page dimensions, or simply "the same as every other document in the file." Your content is scaled to fit the target and centered, and pages that are wider than they are tall automatically receive the landscape version of the size you chose, so nothing gets squeezed.
Use a percentage when the change is relative: shrink a wall poster to 25% for a handout, scale a booklet up 130% for easier proofreading, or nudge a page down to 95% to create breathing room around dense content. Percentage mode multiplies both dimensions equally, so a 300 x 600 mm page at 50% becomes exactly 150 x 300 mm.
The A4 vs US Letter problem
A4 (210 x 297 mm) and US Letter (8.5 x 11 in, roughly 216 x 279 mm) are close enough to look interchangeable and different enough to cause real trouble: Letter is a little wider, A4 a little taller. Print an A4 document on a Letter printer without adjustment and the bottom of every page risks being clipped; the reverse trims the sides. If you regularly exchange documents between Europe and North America, converting the PDF itself to the destination size - rather than trusting every recipient's printer dialog - is the only way to guarantee what arrives is what prints.
Documents with mixed page sizes
PDFs assembled from many sources - a merged bundle of scans, invoices, email exports and photographed receipts - usually end up with a different page size on every other page. Print such a file and the printer either pauses on every size change or scales pages unpredictably. Resizing the whole document to one standard size produces a uniform, professional file where every page prints identically. This is the single most common reason legal teams and accountants resize PDFs before submission.
When another tool is the better fit
Resizing scales everything on the page. If what you actually want is to remove something - trim scanner margins, cut a page number strip, isolate one figure - that is cropping, and Crop PDF does it without shrinking the content you keep. If pages are the right size but sideways, Rotate PDF fixes orientation without touching dimensions. And if the file is simply too heavy in megabytes, Compress PDF reduces storage size while leaving page dimensions alone. The four tools are deliberately separate so each does one predictable thing.
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