1. Enter reading page -> Tools ; 

2. Select Hyperlink  on the toolbar, then you can drag a range for the link. The range is the area where the link is active;

3. There you can choose to redirect it to different destinations: Page, URL and Email:

    1) Page: Enter a page number of the current document so that you can be navigated to that page directly;

    2) URL: Insert a link to the destination web page;

    3) Email: Provide an email address to send emails easily.

4. Click Go to finish the setting;

5. If you want to make the link area visible or invisible, click Page Display  and turn on or off Highlight Links, or you right-click anywhere in the PDF and tick Highlight Links.