Having moved from Germany to Austria I was pleasantly surprised that they have a functional national ID system that you can use to sign PDFs with a qualified electronic signature. Within Austria, they have been accepted everywhere so far.
Usually sending them the following helps them be less stubborn:
> Gemäß Artikel 25 eIDAS-Verordnung hat eine qualifizierte elektronische Signatur die gleiche Rechtswirkung wie eine handschriftliche Unterschriftund wird in allen Mitgliedstaaten anerkannt.
Doesn't work always, but the times it doesn't I usually find a competitor that does prove to be more cooperative pretty easily!
https://www.handy-signatur.at/hs2/#!sign/single
When I tried sending such a document to a German insurance company, they refused to accept it. I ended up faxing the document :/