Would you provide more information about the problem?
Do you have a Windows or Mac desktop/notebook computer or a mobile device (iPad, iPhone, Android tablet or phone)?
What is the version of the operating system on your computer/device?
Does the PDF document show a sign-in dialog? Does it ask you to enter username & password or just password? Do you see an error message after you try to sign in?
Would you take a screenshot and post it to your next reply? (Please note that the Adobe forums do not accept email attachments. Please sign in and add a screenshot to your next reply via the web interface instead of attaching it to your email reply.)