From those requirements especially MS Office & Adobe they should stay on window.

If its as old as a t400 they will struggle with modern browsers & high modern web 3 websites full of JS frameworks which might cause problems with o365

The pdf requirements mean your gonna have to do a lot of configuration & program selection especially for annotation

Debian 12 is very stable & a good choice especially for older hw which most arch based distros never test on, thus rolling releases are far more prone to breakage . Plus Debian has plenty of online resources & updating it is as simple as 2 lines sudo apt upgrade && sudo apt full-upgrade