The Cordova File plugin is used by the app, it's not in Moodle. It's a plugin we need to be able to work with the files in the device.
I did some tests with that file and I was able to import them to the app successfully. Can they import those files with other apps (e.g. Adobe Acrobat Reader)? Also, can they share files from other apps (like Safari or Acrobat Reader) to the app?
It's the first time I see that error :/ The only thing I can think of is that maybe it's a problem with file permissions, but it's really weird that it only happens with these 2 students.