From what I recall, Okular seems to handle a PDF's form data implicitly, transparently saving the data somewhere upon closing the PDF. When 2 instances of Okular are viewing the same PDF, the form data from the last instance to be closed is the data the gets saved, without warning.

I needed to fill out a long form while referencing instructions placed in the same PDF after the form; rather than scroll between the instructions and the form (or figure out the 'correct' way to view both at the same time), I simply opened the whole PDF again (`okular path/to/the.pdf' &), so that I could flip between the instructions and the form using my window manager. When I was finished, I closed the form and then closed the instructions, and then realized that all of my work must have been destroyed, which  it was indeed.

I find it odd that Okular doesn't treat such form data more traditionally, asking the user if data should be saved, and checking whether the file to which it would save has changed already, etc; perhaps Okular should allow the user to specify an explicit form data file, too. As it is now, It feels like handling form data was kind of tacked on using some hack within an existing feature (such as the implicit saving of which page the user was last reading).

Reproducible: Always

Steps to Reproduce:
1. okular path/to/the.pdf &
2. okular path/to/the.pdf &
3. Edit a form in one instance, close that instance, then close the other instance.
Actual Results:  
Form data is that of the instance which was closed last.

Expected Results:  
Form data is not necessarily that of the instance which was closed last.

Okular should check to see whether data should be saved, and indeed whether data has already been saved by something else.