A4, Letter, A3 and Legal PDF page sizes explained
Choose the correct target page size and avoid accidental stretching.
A4
A4 measures 210 × 297 millimetres and is widely used for business and government documents outside North America. It is a sensible default for applications, certificates and general paperwork in Japan and many other countries.
Letter
US Letter measures 8.5 × 11 inches. It is common in the United States and Canada. A Letter document placed directly on A4 may have different margins, so fit it proportionally instead of stretching it.
A3
A3 is twice the area of A4 and is useful for larger diagrams, posters and two-page spreads. It can produce a larger PDF viewer canvas even when the content itself is not high resolution.
Legal
US Legal measures 8.5 × 14 inches. It is longer than Letter and is used for some contracts and legal paperwork. Do not choose Legal merely to fit a long image when the receiving organization expects A4 or Letter.
Always preserve proportions
When changing page size, scale the original page uniformly and center it. Stretching width and height independently distorts text, signatures and photographs.