The law states:
"When a web page requires that an applet, plug-in or other application be present on the client system to interpret page content, the page must provide a link to a plug-in or applet that complies with everything from Alternative Text through Scripts covered in this tutorial."
If you use content that needs a plug-in to be viewed, you must provide a link to the required plug-in. The link to the plug-in must be an accessible page, and the plug-in itself must be compliant with assistive technologies.
In addition to linking to the applet or pluggin, any media and e-documents (pdf, word, excel, etc.) must be made accessible. For more information on creating accessible materials see the e-documents section on the Accessibility Web site.