[suggestion] Warn user if PDF is interactive form

[Shohreh]

(I haven't found how to check if the suggestion has already been made in the forum)

Hello,

Since SumatraPDF doesn't yet support forms, I suggest at least warning the user when opening such files like Foxit Reader does.

I was sent a form PDF recently. Since Sumatra just displayed it with no warning, I thought it was just bad design and painfully edited it in LibreOffice Draw… before being told by the sender that I could have filled it directly :-/

Cheers,