Safari won't load PDF forms even if Adobe Reader is installed..

amper_x,

Thanks for letting us know.  Have you tried creating a new user on your Mac to see if the issue persists there? If not, please give that step  a try, and let us know the outcome.

Change Users & Groups settings on Mac

Click the New Account pop-up menu (you may be asked to enter your password), then choose a type of account.

* Administrator: An administrator can add and manage other users, install apps, and change settings. The new user you create when you first set up your Mac is an administrator. Your Mac can have multiple administrators. You can create new ones, and convert standard users to administrators. Don’t set up automatic login for an administrator. If you do, someone could simply restart your Mac and gain access with administrator privileges. To keep your Mac secure, don’t share administrator names and passwords.

* Standard: Standard users are set up by an administrator. Standard users can install apps and change their own settings, but can’t add other users or change other users’ settings.

* Sharing Only: Sharing-only users can access shared files remotely, but can’t log in to the computer or change settings. To give the user permission to access your shared files or screen, you may need to change options in File Sharing, Screen Sharing, or Remote Management settings. See Set up file sharing and Share the screen of another Mac.

* Group: Groups allow multiple users to have the same access privileges. You control a group’s access to your shared folders by setting access permissions in the File Sharing options in Sharing settings.

See Add a user or group.

Performing this step above will help us to further isolate the problem you're experiencing.

Thanks for using the Apple Support Communities.

Cheers!

Hi amper_x,

We'd like to share some information to help with getting a solution for viewing your PDFs on Safari. We would recommend looking over Allow or block pop-ups in Safari on Mac - Apple Support to see if you need to allow this if this is registering as a pop-up from the site. If this does not help, let us know if this happens with all sites or this specific one.

Thanks for using Apple Support Communities.