How to Resize a PDF to A4
Converting a US Letter PDF to A4, or the reverse, comes up constantly for anyone sharing documents internationally, since the US almost exclusively uses Letter while most of the rest of the world uses A4.
The core size difference
US Letter is 8.5 x 11 inches, while A4 is 8.27 x 11.69 inches, meaning A4 is slightly narrower and noticeably taller. Because the proportions differ, not just the total area, a naive resize can leave a strip of empty space at the bottom or cut off a small amount of content at the edge.
Choosing scale vs. crop-and-pad
A scaling resize shrinks or stretches the entire page proportionally to fit the new dimensions, which keeps everything visible but can slightly alter margins and spacing. An alternative approach centers the original content and adds or trims blank margin space to fit the new page shape, which better preserves the original layout's exact proportions at the cost of extra white space.
Checking your margins after resizing
After converting, always check the margins on both the top/bottom and left/right edges of the resized document, since the size difference between Letter and A4 tends to show up most in vertical spacing rather than horizontal.
Preventing this next time
If you regularly send documents internationally, setting your source document (in Word, Google Docs, or similar) to A4 from the start avoids needing to resize the PDF after the fact, and produces a cleaner result than any after-the-fact conversion.
