Nitro PDF Pro supports documents with file attachments. To link to another document, see Links.
Read and Extract File Attachments
View a list of all the document’s attachments by clicking on the Sidebar
and choosing Attachments
View an attached file by double-clicking on it in the sidebar.
Right-click on the file to extract it and save it or to preview the contents.
Adding and Deleting File Attachments
(Advanced feature of Nitro PDF Pro). See Adding File Attachments.
Note: Not all PDF apps support attachments. A PDF re-saved in an app without support for this feature will erase the annotations. This includes Preview in El Capitan and earlier.