If you print an A4 size PDF from the Adobe Reader, choose "Fit" rather than "Actual size" and the result should fit nicely on letter paper.

It depends on your printer if it all fits, because "Actual size" prints A4 documents very close to the edge (bottom edge, especially) of letter paper, and for some printers, it is not possible to print within 1/2 inch or a centimeter of the bottom edge. "Fit" leaves enough margin all around the page when printing. The scaling is only something like 95%. It is true that many amateur engravers use font sizes that are too small, especially with lyrics.

For some works in CPDL, the source files (Finale, Lilypond, etc.) are available. With these, it is possible to change the paper size specification and format the score for US paper.

In Finale, the "default" staff height is 24pt (about 1/3 inch). However it is common to change the staff height to something like 18pt (1/4 inch) or even as small as 16pt (2/9 inch). If the normal lyric font size at 24pt is 12pt, then at 18pt a 12pt font will appear to be a 9pt font (due to the 3/4 size reduction); hence, at a staff height of 18pt in Finale, one should set the lyric font size to 12pt x (4/3) = 16pt to have the actual score display lyric text at 12pt.

In practice, however, a lyric font will normally be chosen to appear at about 10-11pt in good choral engraving.

If you want lyric text to appear at about 11pt, then with Finale staff height set at 18pt (3/4 reduction), you need to set the lyric font size to something close to 11pt x (4/3) ~ 14pt. For a Finale staff height set at 16pt (2/3 reduction), an apparent 11pt font will be obtained by setting the lyric font size to something like 11pt x (3/2) ~ 16pt. These are the values I tend to use. Other font sizes (eg. staff name fonts) need to be enlarged similarly when the staff height is set at 18pt or 16pt.

Alternatively, when setting lyric font sizes you can select, say, 10pt or 11pt, and check the "fixed size" box, so that the lyrics will remain at the selected font size even when the staff systems are rescaled. I prefer not to do it this way, however, because the alignment of lyrics with notes under this "fixed size" option seems at times not to be as good as it should be.

To summarize: (1) if the Staff Height is set at 18pt, then set the Lyric font size to 14pt (and the Staff & Group Name font sizes to 16pt); (2) if the Staff Height is set at 16pt, then set the Lyric font size to 16pt (and the Staff & Group Name font sizes to 18pt). And, whatever you do, don't use Times Roman fonts, but change them to something like Palatino Linotype or Garamond (I prefer Palatino Linotype).