Right click on context menu on object in 800xA able to open wordpad insted operator note
You may add a Windows Application Aspect to the desired object or object type and give it a proper name. As Windows Application you specify wordpad.exe.
Now the aspect should be in the context menu. Maybe you have to adjust the filter for the context menu if you have set one.
There are no "out-of-the-box" solutions for this. The Windows Application can be used to launch any application using any argument - but the application and argument will have to be statically defined on the aspect. There is also the File Viewer aspect, but I assume it will not work as you wish in this context.
Have you taken a look at the "Operator diary" (Operatörsdagbok) system extension available from Sogeti in Luleå, Sweden?