OK, I read the article https://itsfoss.com/pdf-editors-linux/ . First I tried Okular, available from Synaptic package manager. It did not seem to have an easy way to fill in forms though.
Then finally I tried the other recommendation, Master PDF Editor at https://code-industry.net/free-pdf-editor/ - this worked like a charm! It's closed source code, so that's why I tried the open source options first, but... WOW! With Master PDF Editor I was able to insert text quickly and easily into my form. I have just finished filling in the form, saving it and printing it out. They offer a paid and free version. I used the free version and it did the forms just fine. The paid version has other features as well, but the free one works fine for forms.
Marking this as solved.
Then finally I tried the other recommendation, Master PDF Editor at https://code-industry.net/free-pdf-editor/ - this worked like a charm! It's closed source code, so that's why I tried the open source options first, but... WOW! With Master PDF Editor I was able to insert text quickly and easily into my form. I have just finished filling in the form, saving it and printing it out. They offer a paid and free version. I used the free version and it did the forms just fine. The paid version has other features as well, but the free one works fine for forms.
Marking this as solved.
Using Linux Lite for everything now. I put it on my desktop and my laptop. Woohoo!