vi Editor

Opening up the vi editor in RO mode

view or vi -R

Various methods of exiting the vi editor mode

ZZ to save and exit
:e! to returns you to the last saved version of the file, so you can start over.
:q! to wipe out any changes and exit.
:w! to force write.
:sh to create a shell 
:!rm junkfile
:w <file_name_to_save>

You can also download the apvlv which is a GTK "VI like PDF Reader" as a startup. So, that you can learn the VI editor environment faster.

Auto complete under vi Editor,

In Edit mode type <ctrl-P> and Voila.. it suggests the auto complete by predicting the remaining characters to complete the word from a similar beginning words in your file.

Enjoy your Experience.