With difficulty.
Method 1: Use the full version of Acrobat (or equivalent); save as RTF. It
tries to retain the formatting, with varying success depending on the
complexity. You will at least get all the text. Note that PDF files can be
locked to prevent this saving.
Method 2: Again in Acrobat, select the text, copy and paste to Word. (Also
lockable)
Method 3: Install a generic text printer on port FILE:. Print the document
to that. You'll definitely lose all formattng, but the text should be fine.
Method 4: Trawl the shareware sites for PDF utilities that claim they can do
this.