All programs are a bit different but the end result should be the same.  When you are saving a PDF file from any program that supports printing - Open or create your file with your favorite program and when you're done with your design do a spell check on the document, then follow the instructions below to get a PDF ready to upload.

1. click Print
2. select the drop down menu from the Printer Name
3. Select the Adobe PDF option. 
4. Then click Properties
5. select the Adobe PDF Settings Tab
6. select drop down menu under the Default Settings
7. change it to read PDF/X1a:2001
8. select ok
9. select ok from print window (this will not  start printing; this will just convert your file to PDF.)
10. after you select the location you want to save it
11. select save