How to write a virtual printer driver for Mac OSX

It is called VipRiser - an extensible virtual PDF printer

There is already a driver that does that. VipRiser installs a printer that saves to a file. I use it to 'print out' to a file sheet music I buy online. The existing 'Save to PDF' options at the bottom of the printer dialog won't work because the vendor of the music has disabled this function and you must print to a printer.

For the broadest and simplest support for printing to a virtual printer I use VipRiser rather than using PDF services. PDF Services work in some cases but many sites are preventing the use of PDF Services.

Rather than writing a driver, consider using the PDF Services feature of OS X print dialogs. In either the system-wide /Library/PDF Services or a user's ~/Library/PDF Services directory, you can put AppleScripts, Automator workflows, or symlinks/aliases to applications or folders. Those items will appear in the PDF pop-up menu in the print dialog, and if the user selects the item, a PDF of the file will be placed in the folder or be passed to the application, script, or workflow.