Back up all data.
Quit Safari. In the Finder, select Go ▹ Go to Folder... from the menu bar, or press the key combination shift-command-G. Copy the line of text below into the box that opens, and press return:
From the folder that opens, remove any items that have the letters “PDF” in the name. You may be prompted for your login password. Then launch Safari and test.
If you still have the issue, repeat with this line:
If you don’t like the results of this procedure, restore the items from the backup you made before you started. Relaunch Safari again.