Transfer .bib files

I use the Qiqqa reference manager where most but not all of my pdf files have bibtex metadata, and there are some 'papers' that have metadata but do not have a pdf file attached to them (i.e. are just citations). I wish to import my library into Zotero. I can export a .bib library from Qiqqa and import it into Zotero, but it does not bring the pdf files with it.

1. I wish to have my .bib file from Qiqqa modified so that when I open it in Zotero it brings the pdf files with it.
2. I need to understand how to modify the .bib file so that I can repeat this process on my own in the future.

There are about 6000 papers in the library.