Yes, with both. you can use e.g. the default browser or the htmlviewer package as viewer or a pdf viewer, or...
Fpdoc can generate help for many formats, more than pasdoc.
I use fpdoc for both user help and technical documentation.
It has a somewhat longer learning curve than pasdoc but in the end it is better.
Pasdoc needs sourcecode instrumentation. There is also a documenter written in kol but we probably need to update that. the latter only outputs html.
For professional looking documentation i would ude fpdoc, since once setup correctly it always generates consistent, professionally looking documentation. All FPC documentation is written using fpdoc and it has many output formats.