I'm having problems when I'm in Safari and I open a .PDF file this is what happens
What is my Mac's problem?
Try emptying the Safari cache.
Command + Option + E
Quit and relaunch Safari to test.
If that didn't help, try troubleshooting extensions and third party plugins.
From the Safari menu bar click Safari > Preferences then select the Extensions tab. Turn that OFF, quit and relaunch Safari to test. If that helped, turn one extension on then quit and relaunch Safari to test until you find the incompatible extension then click uninstall.
If it's not an extensions issue, try troubleshooting third party plug-ins.
Back to Safari > Preferences. This time select the Security tab. Deselect: Allow all other plug-ins. Quit and relaunch Safari to test.
If that made a difference, instructions for troubleshooting plugins here.