I’m a beginner myself but did find the answer to this question, by trial and error myself, a couple of weeks back
There’s an “Export” option under the Project menu. It offers various formats. The only one that worked for me (i.e. created a file which, when imported into another project, faithfully recreated the original drawing) was BPMIN2.0.
I’m a little cautious about proffering this advice as I just went in to VP to confirm that and the software is behaving differently to the way it behaved when I successfully exported a drawing (and imported it into a different project).
When I did that, and selected BPMIN option, ALL my drawings appeared as a avalable in the selection box in the lower part of the form. I was then able deselect any I wasn’t looking to export and export just the single drawing I was after.
When I looked at it just now, the only drawings I could see were my few “Business Process” diagrams. None of the others were visible (in this particular project I have about 60 diagrams, most of which are activity diagrams - none of these were available for export)
So it might be that last time I completed a step I’ve forgotten to perform this time, or perhaps the authors have moved the goalposts. But I am faiirly confident that if the drawing you’re seeking to export is available to select in that form, then the BPMIN format will import correctly into your other project.