1.
PDF
Generated from the output by running make pdf in the output directory. In order to get hyperlinks in the PDF file, PDF_HYPERLINKS should be set to YES in the configuration file.
2.
PDF_HYPERLINKS
If the PDF_HYPERLINKS tag is set to YES, the that is generated is prepared for conversion to PDF (using ps2pdf or pdflatex). The PDF file will contain links (just like the HTML output) instead of page references. This makes the output suitable for online browsing using a PDF viewer.