Alphabetize PDF

README.md

 ## PDF
 *Libraries and software for working with PDF files.*
 
+* [Dompdf](https://github.com/dompdf/dompdf) - A HTML to PDF converter.
+* [PHPPdf](https://github.com/psliwa/PHPPdf) - A library for generating PDFs and images from XML.
 * [Snappy](https://github.com/KnpLabs/snappy) - A PDF and image generation library.
 * [WKHTMLToPDF](https://github.com/wkhtmltopdf/wkhtmltopdf) - A tool to convert HTML to PDF.
-* [PHPPdf](https://github.com/psliwa/PHPPdf) - A library for generating PDFs and images from XML.
-* [Dompdf](https://github.com/dompdf/dompdf) - A HTML to PDF converter.
 
 ## Office
 *Libraries for working with office suite documents.*