It depends on your backup method.
First you check out the About iOS Backups link I provided and make sure your backup software includes the backup directory.
I use the built in Time Machine backup software for my iMac. I don't have it tuned on, so I do my backups manually, but every time I do a backup it saves this file, among others. Time Machine creates a series of backups for each file and it's changes. That means I can restore that file from any when; between my first backup of the iPad when I bought it several months ago, to yesterday, the last time I backed up the computer.
Backup software you have may work this way, or differently. If you don't have backup software, be sure to read what it will do, and reviews on how reliable it is, before you purchase.
It's also a good idea to occasionally restore a file, just to make sure backups are working and that you know how to do it.
A manual backup for Time Machine is pretty simple. It's in the menu bar, so all it do is pull down a menu and tell it to backup. I keep two re-occuring reminders (with alerts) in the Calendar to make sure I don't go more than a few days without a backup. As seldom as I change important files, I consider this adequate. Other users may need more or less frequent backups depending on the importance and how often they make changes.
My backups go onto a fairly cheap (but good reliability reviews) 1TB external hard drive.