Preview fails to save pdf forms 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.

Errors:
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.
If you open the link in Safari, you can do a Save As and the pdf is copied wherever you tell it to copy. You can then reopen the file with Preview and it worked fine for me. 

If you can't get it to save as a pdf, go to the print command and when the print window opens there is an option on the bottom left to print file to a pdf. This will create a new pdf file.