Use Adobe Acrobat Pro to create bookmarks in any PDF document. You can create individual bookmarks or have Acrobat automatically create bookmarks that correspond to headers in the document.
Open the PDF you want to modify with Adobe Acrobat Pro and then open the Content Editing menu on the right side of the screen.
Click at the beginning of the line where you want to create the bookmark and choose Add Bookmark from the Content Editing menu. The Bookmarks navigation pane opens on the left side of the screen.
Double-click Untitled in the Bookmarks navigation pane and type a new name for the bookmark.
Repeat the process for other bookmarks you want to add. You can reorder bookmarks by dragging and dropping them in the Bookmarks navigation pane. To arrange the bookmarks in a hierarchy, drag a bookmark underneath another bookmark to create a parent/child relationship.
If the PDF document contains embedded headers, choose New Bookmarks From Structure... from the Bookmarks Navigation Pane to automatically create a bookmark for each header in the document.
If you don't have a license for Adobe Acrobat Pro but you have a license for Microsoft Word, you can create the bookmarks in Word and then save the document as a PDF. The bookmarks convert automatically with the document text.