I found a way to "solve" my problem :
when I copied my .txt files from my external hard drive, the rights of files was 777 (rwxrwxrwx), and when I changed it to 664 (rw-rw-r--) it solved my problem. Now I can open files from the desktop by double click, select and Enter, or right click and "open".
There is still a problem with the menu option "open with..." : it opens directly with the default program without asking witch program I want to use.
There is still some files that are not opened (those with rights 777 (rwxrwxrwx), so I leave the subject as it is.
I found a way to "solve" my problem :
when I copied my .txt files from my external hard drive, the rights of files was 777 (rwxrwxrwx), and when I changed it to 664 (rw-rw-r--) it solved my problem. Now I can open files from the desktop by double click, select and Enter, or right click and "open".
There is still a problem with the menu option "open with..." : it opens directly with the default program without asking witch program I want to use.
There is still some files that are not opened (those with rights 777 (rwxrwxrwx), so I leave the subject as it is.