The most efficient method for adding internal links to a PDF document is to use Adobe Acrobat's Edit PDF tool. First, select the Tools tab and then click on the Edit PDF icon in the Tools Pane. Next, select the Link down arrow in the Edit PDF toolbar and choose either Web or Document Link from the dropdown menu. The selection arrow cursor will then turn into a crosshair-style cursor. To create a link, simply drag a rectangle over the area where you want the link to be active. In the Create Link dialog box that appears, choose your link appearance and other options as desired. Finally, click OK to add the link to the PDF document.