Is it possible to edit / modify an already-made PDF file with such problems like Adobe 5.0?

if you use adobe acrobat (not reader) then you should be able to as long as the file is not password protected.

atleast i think you can... can anyone verify this..?

That's correct WHW.

There are certain programs that can get around the password protection....

But, your ethics are your own business :)

You need Acrobat Distiller to do it.

Acrobat, full version. Distiller is simply an addon to other applications and won't allow you to read and edit files.