You can open a PDF attachment and make changes to it—if you have permissions—and your changes are applied to the PDF attachment.
For other types of file attachments, you have an option of opening or saving the file. Opening the file starts the application that handles the file format of the attachment—you must have that application to open the attachment. Any changes you make are not applied to the attachment. Instead, save changes to the file, and then reattach it to the PDF document.
Open an attachment
In the Attachments panel, select
the attachment, and then click Open or choose Open Attachment from
the Options menu.
Save an attachment
Delete an attachment