Generate Output Files...
Under the 'Home' tab, click 'Project' and select "Generate Outputs". Click on the check box for your outputs. In this case, you should select "Schematic Prints". Click 'Generate' at the bottom and there you go. You can view your file by highlighting the item and clicking 'View'. It's nice to also have PCB Prints and PCB 3D Prints in your PDF as well. Mess around with this a little and you will have nice documentation for your project.
A nice feature of Generating Outputs is the ability to select a component in the PDF file and have it show you all of the attributes of that component.
I hope this has been helpful.
Alternatively, buy WinPDF.
It works well on any app to generate PDF files.
Not affiliated, just a happy user for many years.