From the Permissions disclosure:

  >full network access
  >run at startup
  >prevent device from sleeping

Guess is they're selling user's PDF reading activity data.

PSPDFKit CTO here. We're not selling any user data, PDF Viewer exists because we sell an SDK and having a great app in the store makes it 1) easy to showcase the SDK to potential customers and 2) gives us a broad user base that tests the SDK and gives feedback for free.

Misbehavior by other apps makes such permissions a red flag to some of us.

Prime offender: Amazon Music. Latest rev AFAICT has no "Quit". Have to resort to Settings->Apps->Force_Stop to get its clutter off the screen.

I don't know that this isn't to somehow collect up user data, but this could be to showcase PDFs with embedded video. All my experience with the company has suggested they're on the up-and-up, though.

Disclaimer: I've used the company's SDK fairly extensively in my own product (but I'm not otherwise affiliated with them).