PDF files can take attachments, just as e-mails do. Attachments and their options are shown in the Attachments panel in the Panel area.
Open this panel with this icon in the Panel bar. Close it with the icon top-right in the panel.
To add attachments
Click the Add button inside the Attachments panel, select one or more files and click Open.
To delete attachments
Click the Delete button to remove selected attachments from the PDF. Note that this will not remove such files from your computer, only detach them from your document.
To open an attachment
Select it, click the Open button, set opening preferences in the dialog box and click OK.
The attachment will open in its associated application.
Click the Save button when you are done with attaching files.
Click the Options tool to access the above commands through a drop-down list; you can also have the attachment panel shown by default whenever the PDF document is opened, enter or edit attachment descriptions to tell PDF recipients what they contain and also reset the list of allowed and disallowed attachment file types.
Note
Attachments can also be added to PDF files as annotations at a particular location within the document. If you flatten a PDF you can choose to delete attachments that are annotations leaving only an attachment icon, but files attached directly via the Attachments Panel are not removed by flattening. By contrast, during document inspection (Remove Document Elements in the Security ribbon) you can choose to remove all files in the Attachment panel list, and by removing comments, all files attached as annotations can also be removed.