How to Change a PDF's Page Size (A4 to Letter and Back)
A contract drafted in the US on Letter paper prints with clipped footers on an A4 printer in Europe, the Middle East or Asia, and an A4 report does the same on a US printer. A bundle of documents with mixed page sizes looks untidy and prints unevenly. Changing the page size fixes both, and it is a different job from making the file smaller.
Page size is not file size
'Resize a PDF' can mean two things. Changing the page size (A4, Letter, Legal) changes the sheet the content sits on. Making the file smaller in megabytes, for an email or upload limit, is compression. For the second, use Compress PDF.
Change the page size
Open Resize PDF and add the file. The tool shows its current size. Choose the new one: A4 (210 × 297 mm), Letter (8.5 × 11 in), Legal (8.5 × 14 in), A3 or A5. Leave Orientation on Follow each page to keep each page's own orientation, or force Portrait or Landscape. Download the new file.
What happens to the content
Each page is scaled to fit the new sheet and centred, so nothing is cut off and letters keep their shape. Letter is a little wider and shorter than A4, so moving between them leaves a thin white margin on two sides rather than stretching the text. Going from A4 down to A5 shrinks small print, so check it is still readable.
Trim margins or fix sideways pages
If you want to cut away white margins rather than scale the page, use Crop PDF. If some pages are sideways after scanning, Rotate PDF turns them. A bundle with mixed sizes becomes uniform in one step, because every page is fitted to the size you pick.