The Unable to save as PDF error will come up if one or more protected documents are present when creating a Closing Report on the Reports tab:
When the error occurs, the first step is to find which document is password protected. Open all the documents that are on the Closing Report tool and look at the titles to find the one(s) that say (SECURED). These are usually PDF forms created by L&I (Encumbrance, Accountability Agreements, etc.) or somebody else outside your organization:
To fix the protected document, when it is open, go through File > Print:
Choose Microsoft Print to PDF option from the Printer drop-down:
On the Save Print Output As window, select where the document should be saved, fill out the title, and then Save:
The document that is saved on your computer is the one that should be uploaded to Gardiant and should replace the protected document on the Closing Report tool.
You can now try saving the Closing Report again.