How do you save the model as PDF?
To save the diagram as an image in PDF, download and install a PDF print software (from outside of Toad, i.e. PDF reDirect, Adobe, etc). Once installed, within Toad, go to File | Print, and select the PDF printer installed.
Note: This doesn't actually send to printer. This saves as PDF. Once saved, the file can be opened and printed from any program available that works with PDFs.