> import did not work.
That is too vague. What exactly went wrong? Until now I experienced webtrees accepts nearly everything you throw at it that even remotely resembles a GEDCOM file, so "did not work" is unexpected. Especially since the developer of PC-Ahnen claims he exports compliant GEDCOM files.
It's probably a bit too much to ask you to share the GEDCOM file you received. But could you at least show us the first dozen lines containing the header? I'm thinking it could be due to the text file encoding (see
www.pcahnen.de/html/DatenaustauschGEDCOM.html )
I got somewhat intrigued and found out PC-Ahnen is a 16-bit only Windows application. No further comment.
It would take me some considerable effort to install and run it myself to see how non-conformant the GEDCOM file is it produces.
Then it probably depends on what GEDCOM "features" exactly were used. Since you mention sources, the stored data is presumably a bit more complex than just relations, names and dates.
> What can I do?
I expect there are structural shortcomings in the GEDCOM file. These could probably be repaired with a good text editor that has search / replace facilities with regular expressions. Determining what was actually supposed to be written into the file could require it to be loaded back into PC-Ahnen itself.
How many persons are in the file? Can you install & run PC-Ahnen yourself? Then you can import the file there and just copy-paste whatever you want. That's the approach I'd take if the GEDCOM contains less than say 100 individuals. I estimate it takes about a day of work to just copy-paste all basic data (names, dates, places, relations) for less than 100 persons.
But since you got it from a cousin, the chances are big there is a huge overlap with data you already have. I'm personally not a fan of merging trees and merging individuals & families from different authors. The place hierarchy could be different, etc. I'd prefer to review all the data before entering it into my own system. Manually.