Where is the interface part for importing parts of a different PDF in my document?
The PDFCreator application only generates PDF files based on your opened documents. You will need PDFArchitect (an application from the same developer). PDFCreator is used only for creating PDF files, while PDFArchitect is used to modify them, therefore the INSERT function is also available.
How to insert: http://www.pdfforge.org/pdfarchitect/modules/insert