I don't know where iPad contacts live. Are they in iCloud? There might be an iCloud app for Windows 10 that would let you get them into your PC.

Regarding your Windows 10 reinstall, did you use the built-in Windows 10 Reset feature that preserves your data? That often would be in a folder called

C:\Windows.old

Do you see anything like that?

Yes, I used the reset feature. I will for the C:\Windows.old folder. I stupidly thought that the address book would be saved and a program that backed Thunderbird up.

Kbarkhouse said

Yes, I used the reset feature. I will for the C:\Windows.old folder. I stupidly thought that the address book would be saved and a program that backed Thunderbird up.

Where did the backup program store its data? Perhaps somewhere that wasn't save from "reset"?

If you find

C:\Windows.old

on your system, turn on viewing of hidden files and folders:

https://support.microsoft.com/en-us/help/14201/windows-show-hidden-files

Then explore up this path:

C:\Windows.old\Users\Windows-user-name\AppData\Roaming\Thunderbird

Your data is here somewhere. I think this article might help: Profiles - Where Thunderbird stores your messages and other user data.

Thanks, I will let you know how I make out.

How do I export my address book from one computer and import to another one?

Andrew M. Rankin II said

How do I export my address book from one computer and import to another one?

http://kb.mozillazine.org/Moving_address_books_between_profiles