Variables in loaded dynamic text

How can i subtend variables in text loaded from a .txt file into a dynamic textfield, something like:

“this is the text loaded from the something.txt file blab blab blab blaaaaaaaaaab <XVARVALUE> blab blab blab”

Where <XVARVALUE> is the string value of another var.
I know I could have 3 vars and do:

textfield.text = var1
textfield.text += var2
textfield.text += var3

but is there a way of actually calling the var in the .txt file itself, hope that makes sense.