I don't know how helpful this is, but I created a simple RTF file in MS-Word, and then looked at it. I found the following in some of the formatting:
15840 is 1440 * 11
12240 is 1440 * 8.5
A twip is a unit of measurement that is 1440 per inch. I would expect that paperw is paper width, and paperh is paper height. And that the number is the number of twips.
I don't know enough about RTF to know exactly where this plugs into the formatting. I also don't know if it is truely part of RTF. I took the same RTF document and opened it in Word Pad. Word Pad did not support the paperw and paperh.
None of this information may be useful to you if you are using a stock API for creating RTF files.
John R Lick