Replace placeholder in Word document

I have the Problem, that i have more than one characterruns. I Need to replace placeholders like <!test> or <!here>; so i check for These words. But i have Problems when in the run is "<!" and in the next range is "test>". Is it possible to replace over some more ranges? How to do it?
i tryed to manipulate at the end with: 'doc.getDocumentText().replace'. But its not possible to do it in that way... Can anyone help?