I do have the following problem:
I want to create a PDF-File with placeholders (fields??), so that a User is able to upload another PDF that is then shown at the palceholder. Afterwards that "updated" PDF should be saved as a PDF that is not editable. Is this possible?
Best Regards und thanks for help in advance
You certainly can't place a PDF file within a page of another PDF file in the same way you can place one in Word, for example; but with Acrobat you can insert pages from one file in between the pages of another.
That's the right idea, but it's not necessarily an image, it's a form XObject, which could contain images if they were part of the original page contents, as well as text objects and graphics.