How to Resize a PDF to A4
Converting Letter to A4 (or back) comes up constantly for anyone sharing documents internationally, since the US almost exclusively uses Letter and most of the world uses A4.
The size difference
Letter is 8.5 x 11 in, A4 is 8.27 x 11.69 in — A4's slightly narrower and noticeably taller. Because the proportions differ, not just the area, a naive resize can leave empty space at the bottom or cut off content at the edge.
Scale, or crop-and-pad
A scaling resize shrinks or stretches the whole page proportionally, keeping everything visible but slightly altering margins and spacing. Centering the content and padding or trimming margins instead preserves the original proportions better, at the cost of extra white space.
Check both margins
After converting, check top/bottom and left/right — the Letter-to-A4 difference tends to show up most in vertical spacing.
Avoid the problem next time
Regularly sending documents internationally? Set your source document to A4 from the start rather than resizing the PDF after the fact — it produces a cleaner result every time.
