Modulating voices reading in Applescript?

I have seen the

SAY command in many posts but I can't find it in my dictionary in TextEdit nor the ScriptEditor

I would like to be able to read files in textedit assigning various voices with various speeds in each different file.

I found this script

say "Hello my friend" using "Alex"

which works just fine as it is.

Is it possible to create a script which simply calls a text file of choice and

changes the rate and/or the pitch incorporating the terminal commands in applescript?

as

say -v Alex "Hello" -r 200

THIS ISn'T A SCRIPT BUT WHAT I HOPE TO ACHIEVE

CHOOSE FILE WITH PROMPT

TELL APPLICATION TO

SAY CONTENT OF FILE

using "Alex"with rate 100

Thanks a lot