I recently wiped my computer without backing it up because it was overwhelmed by viruses, and I just bought a new CD, which I planned to put on my iPad 2. The only problem is that the computer is now recognized as a new computer, and wants to erase all my non-apple bought content. Is there any way to avoid this?
IPad – How to you put new songs from a computer to an apple device after you wiped the computer and it counts as a new one
data synchronizationipad
Related Solutions
In researching solutions, I found this discussion at apple.com in which somebody suggests "damaging" the iTunes library. This lead to a very useful post which discusses how iTunes uses the data it has to recreate what it doesn't have and gives instructions on how to damage (without deleting) the file -- spoiler: erase the data, leave the file.
Fortunately, I had backed up the iTunes files before I recreated the iTunes library.
I copied my backed up files back into the iTunes directory and launched iTunes and rebuilt what it needed to. There were no apps listed in the Apps display though.
When I connected my iPad, iTunes didn't complain about this being an unknown device. As it started to sync, it prompted my to transfer purchases (i.e. the apps on my iPad which didn't show in iTunes) -- but with no hint of having to erase anything. The sync took longer than normal, but everything is there and I can even find the songs which were originally hidden.
iPad is fine, will sync my wife's iPhone tonight.
I do this all the time - introduce an iOS device with content to a new library (whether it's on the same or a different computer).
In your case, if you simply don't sync until you reintroduce the last good backup of iTunes then everything will be fine again. But let's assume you don't want to do that and continue with the question as asked.
You can cancel the sync when the warning about erasing the content appears. At that point go and deselect the automatic sync option so you have time to transfer the documents. 
Then you can use the File menu
Transfer purchases from "device" to get all the "apple iTunes store" content into the new library. This is a smart merge so you don't get any duplicates. Lastly, inspect the Apps tab to check for any third party data you might want to transfer. 
I also use the iBooks email to get a few PDF off an iOS device but you may want to look into trying and later purchasing PhoneView which lets you move documents to/from your device to a mac with ease. It's very powerful and goes far beyond what iTunes allows.
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Best Answer
You can use a product like iExplorer to first copy your music off of the iPad on to the computer. Then use the copied music to rebuild iTunes and then when the music on the iPad gets wiped it won't matter as it will get replaced with what you copied to the computer and added to iTunes.