If you have a WordPress site and you like to share your pdf document online with certain people ( such as with your clients ) you need to protect your file.
Be aware most WordPress plugins only protects your WordPress content. They do not protect and single images or uploaded files so if you enter and exact URL to in image file it will still be accessible.
To overcome this problem you have two options:
1. You may use password protected login page
2. You may upload password protected pdf file online
You can create your PDF file with password protection, therefore only people who have the password can read the file. This is a simple way to protect your content.
If you are a MAC user and using pages to axport your file as pdf, it has built in password protection feature.
If you are a PC user there are some softwares allow you to do that.
You may also create online password protected pdf file.
A few links worth to visit: