See also: Attachments ribbon group, Attachments dialog box
Steps:
On the docked split container, click Attachments node.
On the ribbon bar, in the Attachments group, click Add Attachments button. Add Attachments dialog box appears.
Select File option if the file is desktop based or Website (URL) option if the file is web based.
If the file is desktop based then, beside File Name field, click browse button and navigate to the appropriate file.
If the file is web based then, beside File Name field, type URL of the file.
Click Save and Close.