Why do I have to sign in EVERY time I open a .pdf?

Hello,

Thank you for reaching out and sorry for the trouble.

As you get the sign-in prompt every time you try to open the PDF, please try the troubleshooting steps suggested here: https://community.adobe.com/t5/acrobat/acrobat-keeps-asking-to-sign-in/td-p/11525698?page=1 

Check if that helps.

If the issue still occurs, please share the application and OS version number.

It would be helpful if you can share the video of the issue occurs.

Let us know if you need any help.

Thanks,

Meenakshi