THe most annoying is that when I restore my ipad, I can see them for , like, two seconds before they disappear.
I'm guessing here since I'm not sure why you can see them only 2 seconds.
Do you have iCloud ON?
Settings > iCloud > Documents & Data?
Anyway, you must have gotten it from somewhere, can you not download again?
Is it from your mail attachment? From a website? etc..
>Well, we learn from it don't we?
What kind of 'Support' is that!
All my stuff was lost as well on upgrading to 6.1 and synching my ipad. Wiped the lot off it without warning!
If it helps, my pdf's are all in an 'Unknown Artist' folder in my music library on the PC. Windows luckily.
- E:\Documents\Music\iTunes\iTunes Media\Music\Unknown Artist\Unknown Album
Why!? Wasted ages looking for them. Maybe yours are there too
I also had to go back into itunes-Preferences-General to re-tick 'Books' Why was it unticked for no good reason? Further frustrating waste of time finding this out. I didn't know why it disappeared from the sidebar for no logical reason either. Now I've got to waste more time putting it all right again. What a complete mess-up!
And where are all my books? My DRM free ones in iBooks on the iPad. Gone. I haven't found those yet
Well, I've found where my books should now be, each author now has their own named folder installed in my music library folder, mixed in with all the artist folders, with sub folders in each one for each book. So far so good, but sadly all the folders are empty!
All my books remain gone.
Since transferring back all my pdf's back to itunes, then back to the ipad, I find itunes has made yet another new folder in the Music Library - Books. It has duplicated all the pdfs in here
I expect when I transfer my books back to itunes, it will now put them in the Books folder leaving all the empty folders scattered throughout the music library as mentioned above. So it looks as if the ipad is now looking for a folder called 'Books' on my ipad. It's just a pity that this wasn't all done cleanly and instead caused such a waste of time and effort
dont really know if its still needed, but as @andiiman mentioned above,
go to: \Documents\Music\iTunes\iTunes Media\
there should be a folder named "Books" there with all lost pdfs and epubs inside
hope it helps, since it happened to me both on the iOS 5 --> iOS 6 update and over again now on the iOS6 --> iOS 7 update