Aide PDFCreator
 
 

I have selected letter (8,5"*11") as paperformat in Word/Excel, but the generated PDFs are in A4

Word/Excel have an option which automatically scales the letter format to A4 or vice versa.

You can find it in Word-Options->Advanced->Print->"Scale content for A4 or 8.5"*11" paper sizes".

Deactivating this option allows you to create Documents in letter format.