Is It Only

[Bounda 0]

is it only possible for autoit to use the run function to target .exe only files?

[cppman 1]

yep...

http://www.autoitscript.com/autoit3/docs/faq.htm#6

but, it can always be started with another program like

run("notepad.exe textfile.txt")

[greenmachine 4]

Not quite. You could use Run (@Comspec & " /c start somefile.txt") and it would open somefile.txt in Notepad. In other words, the "start" command of the cmd prompt can be used here.