Here is a short list of popular paper sizes, in points:
A0 2380x3368
A1 1684x2380
A2 1190x1684
A3 842x1190
A4 595x842
A5 421x595
A6 297x421
Remember, the PDF standard is marvellously flexible in that it allows you to have varying page sizes; don't feel constrained to stick with A4 all the time.
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