Step 4 : Options dialog box opens, tick Encrypt the document with a password to set the password for the PDF document.
Step 5 : Then, the password settings dialog box appears. Please enter the password and redefine the password in the empty box then click OK to complete
Finally, you just need to click Save to save the file as PDF again.
So, you just created the password for the PDF file using Microsoft Word. Very simple, right?
Good luck!