You may want to password protect a PDF file to make it more secure and to protect it from someone else opening it. It also makes sense to secure the PDF document if it contains sensitive and confidential data. Better to be safe than sorry!
How to Password Protect a PDF
There are several ways to password protect a PDF file. One of the most easiest ways to password protect a PDF is to upload the PDF file to pdfprotect.net ; Set a security password and export it as PDF again. The service can be used to password-protect files up to 10 MB in size and is pretty useful to password protect general documents.
The site also provides option to use a higher or a lower encryption strength.