One obvious approach to parsing the HTML for what you're calling "paragraphs" is based on the two main kinds of HTML tag.

There are block tags, which create a linebreak above and below, and inline tags which flow with the text.

The DTD for HTML will tell you which is which: http://www.w3.org/TR/html401/sgml/dtd.html If you feel like working through it.

Complications of course arise because there can be blocks inside blocks, and because CSS is allowed to re-define the block/inline setting to suit the author.