Gmail asks for PDF password

I generate all invoices without password: in fact, I can open the generated PDFs as normal.
If I send them throught Gmail of Inbox, the recipient can’t open them directly as attachment, since he’s prompt for password! It happens even if I try to recover them from the “sent” folder.
But if I download them on my pc again, they work normally again.

Hello Friend,
This problem is fixed in update 1.4.7. However, you can also correct yourself.
Enters this link:

Greetings from Peru.