Depending on whether DineroRegnskab/PdfiumAndroid@9236635 actually updated the libraries to March 2021 (M90) versions, which is unclear to me, there are at best 5 known security issues, at worst ~80.

See:
https://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=PDFium
https://divestos.org/misc/appsec.txt