I have had this problem for a long time. We buy lot of digital books and store them to Google Drive from where I then access them with Adobe Reader with my tablet. Sometimes files get corrupted, they may be readable for days and then stop working. The file cannot be opened it is damaged or corrupted. The version in the Google Drive is also corrupted and has to be replaced. The corrupted version varies videly with the file size compared to the original, sometimes it is even only half the size.
I must add that the file is not touched by anyone or thing else than me with my tablet, and this has not happened with any other usage of those books.
Any help would be appreciated. I run the newest application version.