Use the bookmark manager of Foxit Reader to add bookmarks and sub-bookmarks. Please refer to the following steps for specific operations. The demonstration software is Foxit Reader.

1. First, open the target PDF file with Foxit Reader on your computer, and click the bookmark management icon on the left side of it.

2. Then pull the document to the specified page and click the Add Bookmark button.

3. Then name the bookmark, then drag the page to the position that needs to be used as a sub-bookmark, add the bookmark again, and name it in the same way.

4. Then use the mouse to drag the sub-bookmark content to adjust it to the target bookmark.

5. After completing the above settings, you can add bookmarks and sub-bookmarks in Foxit Reader.