dompdf is an HTML to PDF converter. At its heart, dompdf is (mostly) CSS2.1 compliant HTML layout and rendering engine written in PHP. It is a style-driven renderer: it will download and read external stylesheets, inline style tags, and the style attributes of individual HTML elements. It also supports most presentational HTML attributes.

PDF rendering is currently provided either by PDFLib (www.pdflib.com) or by a bundled version the CPDF class, originally R&OS CPDF written by Wayne Munro but customized by the dompdf team to improve performance and add features. In order to use PDFLib with dompdf the PDFLib PHP extension is required (available from PDFLib). Using PDFLib improves performance and reduces the memory requirements of dompdf somewhat, while the CPDF class, though slightly slower, eliminates any dependencies on external PDF libraries.