I put the line for Abiword in defaults.list and now assiciation works fine. I also tried with that 'my line' for Leafpad, but still Notes opens .txt files instead of Leafpad.

I have another issue. I have installed FreOffice, which is in Dbus-switchboard associated with .doc and .pps files and that works fine. FreOffice should also handle .rtf files but that's not working in my case, it starts and than hangs on black screen. So, because of that I associated .rtf files with Abiword which works great in File Manager. Now, the problem is when .rtf files are attached to emails. In that case if I tap on .rtf file it initiate FreOffice instead of Abiword (without any yellow banner). Same happens when I tap on .doc attachments, FreOffice starts without yellow banner despite the fact that it's associated with .doc files in Dbus-switchboard. But that's not so crucial, because I want for .doc files to be opened with FreOffice.
Another thing that I have notice is that .abw attachments are handled properly with Abiword (initiated with yellow banner). So, obviously in my case .doc and .rtf attachments are not handled with Dbus-switchboard because of FreOffice installation.

I apologize for all linguistic mistakes I made. Sorry guys, but English is not my native language.