Thank you for your question. Yes, the (newly labelled) "Import Scripture" button on the "Basic" is misleading. That button can indeed import scripture, BUT only if it is in one of the prescribed formats: USFM or USX. In other words, there is a globally-accepted standard for scripture markup, and PTXprint is aware of that standard. Nothing else can be imported. The primary purpose of PTXprint is to help Paratext users create PDFs of their scripture texts.
Given that PTXprint takes (plain) text with appropriate markup and turns it into a PDF, I don't think this program is going to help you, as you already have a PDF. (But how did you create your PDF in the first place? What is the SOURCE of the PDF?) If you were able to convert your source (let's say a Word Doc) into marked-up USFM and saved as plain text files, again with appropriate filenames etc. then PTXprint would be able to use the scripture in that format for producing a PDF.