The process to convert from a DP text with homegrown markup to an HTML file that can be submitted to PG is long, involved, and largely manual as illustrated by these checklists:
It looks like there are some new tools that some people are using
If you're wondering if an HTML file that you have was generated by ppgen, look for the following comment at the end:
</body>
<!-- created with ppgen.py 3.46b on 2015-02-07 02:35:10 GMT -->
</html>
There's another tool called PPQT which has HTML generation built in:
I'm not sure how widely used it is, but I'm guessing less than PPGEN.
Tom