The hardest part of creating a PDF document this way is to keep control of blocks of text. You need to know the height of a block of text in order to handle pagination correctly in multipage documents.

Font Characteristics
Text Rendering Attributes
Calculating the height of a blurb
<?
 pdf_save($pdf);
 pdf_translate($pdf,0,$page_height);
 pdf_scale($pdf,1,-1);
 pdf_set_font($pdf, $font , 12, 'winansi');
 $leading = pdf_get_value($pdf, "leading");
 $height = $inc = 12+$leading;

 while(pdf_show_boxed($pdf, $text, $x, $page_height-$y, 
                     $page_width-2*$x, $height, $align, 
                     'blind')!=0) 
     $height+=$inc;

 pdf_restore($pdf);
?>