unknown iPad backup pw

Without knowing your backup's password you won't be able to restore to it. Did you have an Exchange email account on your iPad ? If you did then it's possible that the account administrator forced the backup to be encrypted - in which case contact them and ask them for the password. If you didn't then see if anything on this page helps you remember it : iOS: Troubleshooting encrypted backups - Apple Support.

But if you can't find or remember your password then you won't be able to restore to the backup, you will have to start from scratch with your iPad.

Did you have a work email account set up in the Mail app on the iPad ? If you did then it's possible that it was an Exchange email account - a lot companies use Microsoft Exchange for their email systems, and the administrator of such accounts can (for security reason) force things such as encrypting backups and having a passcode to unlock a device.

You can sync your apps back from your computer's iTunes, and the podcasts if you have them on it. What you will potentially be losing are any documents or files that you had in the apps (unless the apps use a cloud server to store your content), and, if you had games, possibly their progress (though if they are linked to game centre you might be ok).

For the warning, presumably Apple thought that there is no need to give a warning about a backup being encrypted, the only way that I know that a backup can become encrypted is if you had chosen yourself to make it encrypted (encryption can't be turned off without knowing the password), or if you had an Exchange (i.e. a work) email account and the account administrator is forcing encryption for security reasons.