Example : [i539] (https://www.uscis.gov/system/files_force/files/form/i-539-pc.pdf)
I can fill the form and "Export As PDF..." but I can not save the pdf so that I can continue to fill later.
File > Duplicate : "The file couldn't be saved"
File > Save... : "The document 'I-539-pc copy" could not be saved as 'I-539-pc copy.pdf'"
OS: macOS Catalina (10.15.3)
This happens for most such forms.
And, I don't have admin access to install any other pdf software.