In addition to what Sergey has said .. you should make sure you let the user select the printer prior to running the report to a file:

=SYS(1037)
REPORT FORM MyReport TO FILE MyFile NOCONSOLE
nPages = _PAGENO
REPORT FORM MyReport TO PRINTER PREVIEW NOCONSOLE 

If you don't prompt for the printer first, you run the risk of having the first dummy pass to the file prepared with the default printer. Then when the user prints the final report, they could pick a different printer which has a different printable margin. Most of the time this won't be a problem .. but there's always that one case that can bite you.

Cathy