In my minimal working example I use a pdf_tex file as input. I have been asked to upload it; however, I can only upload the pdf file since pdf_tex is a text file.
Of course, I can paste the content of the pdf_tex file into my question. But what is the preferred course of action here?
I think you should paste the contents of the pdf_tex file into your question. Then all the necessary info will be in the question itself, which is better than relying on external sites, in my opinion.
Note also that if you upload a PDF as an image to the post, it will be converted to PNG, I don't think the original PDF is saved.
To second Torbjørn: It is strongly preferred to include content of your TeX file into your question.
But in almost all cases you should reduce the code to the absolutely necessary parts. This is called a minimal working example or short MWE. We have an own meta question here (see I've just been asked to write a minimal example, what is that?), and you will frequently see, that unexperienced users are asked for a MWE with a text building block containing a link to this question:
Please add a minimal working example (MWE) that illustrates your problem. It will be much easier for us to reproduce your situation and find out what the issue is when we see compilable code, starting with
\documentclass{...}and ending with\end{document}.
