Provide a way to skip pdfium binary download

[Tanish2002]

Is your feature request related to a problem? Please describe. I'm trying to package a app for NixOS. NixOS builds a package in a sanbox where internet access isn't present. Due to this issue, I can't build the app.

Describe the solution you'd like I can think of 3 solutions on top of my head.

1. Either include the pdfium binary with package itself.
2. Provide some sort of way to skip the download process and get the binary from somewhere else (maybe PATH?).
3. Instead of downloading the file it checks a env var which is equal to the downloaded .tgz file, if present then use it instead of downloading..

[CodeDoctorDE]

Hi, is there a good workaround I can use for now?