We are using IPSAPP10 UPD16. Where can I specify to use the “letter” paper size when generating reports?

We generate reports in PDF but from time to time we will print some of those reports and our users are complaining about the fact that all the PDFs correspond to the A4 paper format not letter. Since we do not use A4 paper in our printer, if the user is not carefull, the printer will wait until someone forces it to printer on letter.