Provided you haven't synced since you lost the apps:
Go into iTunes Preferences, the Devices tab, and prevent auto syncing. This will keep the iPad from launching and syncing with iTunes when you plug it in. While you are there look at the date/time on the backup. This will give you and idea of what you are about to restore; and hold in mind that it will restore the data in all the apps, not just QuickOffice.
Plug in the iPad, right click on it in iTunes under the Devices list and choose restore from backup. You will either get the documents back or not.
Alternately you can try one of these programs on your computer to extract files from the backup. I haven't used either of them, they cost money, and the results will still depend on whether the backup still has the files in them. Up to you to decide if the risk/cost is worth the effort.
iBckupBot for iTunes: Backup Manager Software for iPad, iPhone, and iPod Touch (and a few other tricks)
iBackupBot - iTunes Backup Manager for iPhone, iPod Touch, iPad
iPhone Backup Extractor (recover lost data from iTunes backups)
iPhone Backup Extractor for Windows and Mac
To prevent this in the future I recommend getting a DropBox account. I'm pretty sure QuickOffice will let upload/download files from DropBox, which will give you backups of your documents. It is never a good idea to keep important documents in one place, especially something as inherently fragile as a mobile device.
Good luck.