jPDFEditor allows you to attach files to a PDF either as an attachment or as a comment. Attached files can also be opened, saved, and deleted with jPDF Editor.
Attaching a File: How to embed a file to the PDF
Attaching a File as a Comment: Embedding a file with a comment
Opening an Attached File: Opening attached files from the PDF
Saving Attached File: Saving attached files from the PDF
Deleting an Attached File: Deleting attached files from the PDF