Preview in Catalina doesn't allow automatic form filling?
Solution 1:
I've confirmed that this feature was removed in Catalina.
For confirmation you can see on in the Preview User Guide from Apple.
If you check the Mojave (10.14) version, it says "Click a field or a line in the form. A text annotation box automatically appears.".
If you switch over to the Catalina (10.15) version, it now only says "Click a field in the form, then type your text.".
