In a LaTeX project (how) can I use more than one documentclass?

I know that this question is not new but the existing answers I found didn't work out for me. Right now I have a document with document class scrbook which is the master document for my thesis. Chapters are organised in separate tex-files and loaded using the include command. Works perfectly fine. However, I am obliged to put a CV at the end of the thesis. I have created a pretty one using the moderncv class. I would like to include this cv in my existing project such that the basis layout (headlines, . ) don't change and also the page numbering is continued.
But there are the expected issues with loading a tex file of document class moderncv into a tex file of class scrbook . I searched here on stackexchange and found the following answered question: how to deal with multiple titles and multiple documents? and How to use more than one document class which both don't help. The former question is solved by loading a pre-compiled PDF into the document, meaning that page numbering and layout change or have to be adjusted manually. The latter basically refers to the former and also isn't useful to me. Any thoughts and/or suggestions on the problem?

• document-classes
• document-configuration

@Johannes_B The includepdf produces an error "Argument of \Gin@iii has an extra >" but using includegraphics on the PDF worked well, so thank you for that :) Anyway, any ideas on the error?

@sampleuser You could also use most pdf editors to simply concatenate PDFs (if you don't need running page numers/headers over all the documents etc.)

Without seeing your code it is impossible to guess the cause of the error but I'd recommend updating all of your packages as a first attempt to fix the problem.