1. From Thunderbird/Evolution/gmail/wherever: Save message (as .eml).

2. $ sudo apt-get install mpack # or equivalent for your OS - install package
called "mpack"

3. $ munpack message.eml
# bash, multiple files:

$ for f in *.eml; do munpack $f; done Orthunderbird :
- right click on the file -> open with -> open with other applications…

- open the textfield cliking on use a custom command and type :
thunderbird %f and then click on Open button.

I don't know about all of the first stuff, but I just right click on the
file and look for Open with.. then choose Other and select Thunderbird from
the list and tick the box to always open with TB.

Either one works. Depends how you want to learn Linux.

When saving an e-mail message outside TB system I always change .eml to
.txt The file can then be read in any OS.

Changing the suffix will have no effect on the file. The text suffix (in
fact most suffixes) is fairly meaningless in Linux. You can open just about
any file in a text editor. Again, right-click and choose, open with and
choose your text editor, Kate or Gedit. With html email you will get the
html formatting codes, but the text will be intact. With text email, you
won't even get that. Whether it is .*eml or *.txt will be irrelevant.

My wife had a file open. We both tried to scroll up but the document stayed in
the same place and we could not see most of the document, how do we change
this?

Did the mouse control lock up? Did the keyboard page up or page down not work
either?

Not really enough information to go on there - what kind of file and
what program was it opened in ? Also, presumably the scrolling works
elsewhere such as on web pages ??