To paint a string of characters, use the show command, which requires a string argument, and expects the font face and size to have been selected:
/Helvetica 10 selectfont
(any string of text characters) show
The show command creates a path of its own. Look what happens when you combine lines with text:
%!PS
0 0 moveto 306 396 lineto
/Helvetica 10 selectfont
(this adds to the path and moves the current point) show
612 792 lineto
stroke
showpage % END OF PROGRAM
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