Whenever an USB OTG or Bluetooth keyboard is connected, the current activity is reset and reloads.

That means, the currently open PDF gets reloaded and the view gets moved to page 1.

This is really annoying when reading long PDFs.

To fix this, every activity in the manifest file needs this attribute:

<activity android:configChanges="keyboard" />

The only effect this has is it tells Android not to kill and reload the activity when a keyboard is attached. There are no side effects.

Implementing this would take just 5 minutes and would make me a much happier customer.