Hi there. I have the same issue. It hijacks my PDFs. Its not the default app nor have I chosen it to be.
What was your solution for this?
It's very annoying and there are a lot of people with the same issue.

Hi there! I have the same issue.
Bunq is not registered as the default for PDF. But Foxit is.
I even uninstalled Bunq, then open the PDFs. Click on always open with Foxit.
Then install Bunq again, and it overrules my system configs.
It's really frustrating as it opens with Bunq again.
Anyone know how to fix this?