FILEPATH$ = "PATH\TO\FILE.TXT"
IF LEN(DIR$(FILEPATH$)) <> 0 THEN
  OPEN FILEPATH$ FOR INPUT AS #1
    DO UNTIL EOF(1)
      LINE INPUT #1, WORDS$
      THETEXT$ = THETEXT$ + WORDS$ + CHR$(13) + CHR$(10)
    LOOP
  CLOSE #1
  L% = LEN(THETEXT$) - 2
  THETEXT$ = LEFT$(THETEXT$, L%)
  TextBox_Example.Text = THETEXT$
END IF

The above code reads text from "PATH\TO\FILE.TXT" and then outputs that
text to a text-box (TextBox_Example). The "LEN(DIR$(FILEPATH$))" part
checks to see if the file exists. The "CHR$(13) and CHR$(10)" parts
insure that new-lines are printed. The "L%" and "LEFT$" parts act as
"clean-up" because of the "CHR$" stuff.

However, be aware that in programs like VBDOS, you can only have so much
text in a text-box. I would not use this to display long README's or 
books unless you split them into short chapters.