Adobe ACROBAT 3D Manual page 502

Working with attachments created in Acrobat 6.0 or earlier
In Acrobat 7.0, you can view and save attachments in PDF files that were created in
Acrobat 5.0 or 6.0. To ensure that attachments you created in Acrobat 7.0 open in earlier
versions of Acrobat, save a PDF file that contains an attachment with the option to show
attachments when the file is opened.
To create attachments that can be viewed in Acrobat 5.0 or 6.0:
1. Add a PDF attachment to the document. (See
documents.)
2. Do one of the following:
Click the Attachments tab, and select Show Attachments By Default from the Options
menu (selected by default).
Choose File > Document Properties, click the Initial View tab, choose Attachments Panel
And Page from the Show menu, and click OK.
3. Save the PDF document.
Adding attachments to Adobe PDF