Win2PDF Desktop Manage Attachments 
To add, save, or remove attachments from an existing PDF, open a PDF file using "File -> Open" or drag-and-dropping a PDF file onto the Win2PDF Desktop icon and then select "File-> Attachment":
Win2PDF Desktop - Attachment Menu
File → Attachment → Add File...
Adds a file attachment to an existing PDF
File → Attachment → Save All Files...
Saves all file attachments from an existing PDF
File → Attachment → Delete All Files...
Deletes all file attachments from an existing PDF
