PDFCreator is licensed under the terms of the GNU GENERAL PUBLIC LICENSE. But PDFCreator also bundles other components, that can have other licenses. In General: If you only want to use PDFCreator at home, in your business or anywhere else, you may do it freely and in an unlimited way. You may also gives copies to friends, distribute it on all PCs in your company and such things.

Not allowed is selling PDFCreator. It can be also tricky to use PDFCreator from a commercial application and then sell this bundle. Please read the applying licenses carefully, if you plan to do so.

These components are licensed on their own:
GNU Ghostscript: GNU GENERAL PUBLIC LICENSE
RedMon: Aladdin Free Public License (AFPL)
pdfenc: GNU General Public License (GPL)
pdfforge.dll: FairPlay License