Is there a way to see previous purchases?

Yes,

Go into your iOS App Store app on your iPad.

Tap the small round icon in the supper right hand corner.

A pop-up window appears.

Tap Purchases and you will see EVERYTHING you ever purchased from the iOS App Store.

Best of Luck to You!

Then, I am afraid that you will not be able to get this information.

Purchases made through ANY of Apple's online stores are processed through your Apple ID information.

If you never wrote this information down and/or can’t remember it, there is nothing more that anyone here OR Apple can do for you.

Sorry.

Passcode, or iCloud Activation lock?

If the passcode is your issue, the only option other than a third-party tool is wiping the device.

If iCloud is the issue, visit this link:

https://iforgot.apple.com

Hope this helps!

Yes! Visit this website from your web browser and sign into your Apple ID:

https://appleid.apple.com

If purchased via the Apple Store app, previous purchases are listed under Account -> Orders.

I gave them the link because their question says they have an iPad 3rd Gen.

In that case, They will only see there purchased apps.