I'm reading a paper, which is not open access, and I had troubles in some passages there, I would like to ask for help in https://math.stackexchange.com/, for that aim I have to share the paper and not take shots only; is that acceptable? any pieces of advice please?
The abstract of the specific 1979 paper you asked about is written in French, so it would be helpful to identify whether "open access" is so much a barrier to discussion here as content written in a language other than English.
I think Xander Henderson identified the generic difficulty to asking "more than one question" about a technical paper. As the Help Center FAQ puts it ("What types of questions should I avoid asking?"):
Your questions should be reasonably scoped. If you can imagine an entire book that answers your question, you’re asking too much.
If your motivation for asking the question is “I would like to participate in a discussion about ______”, then you should not be asking here.
However, if your motivation is “I would like others to explain ______ to me”, then you are probably OK. (Discussions are of course welcome in our real time web chat.)
My advice is therefore to use a fine grained approach. Start with Questions you are able to formulate yourself, and whose Answers you will be able to digest and Accept with your current understanding. The process of breaking up a lengthy paper into a series of comprehensible segments will no doubt be time consuming, but it will reward your patience and will likely produce Math.SE content that will have substantial interest for Readers in the long run.