If your PDF contains any password security, it will not be accepted.
If you receive this error message"ERROR: Document contains code which may cause an external action (such as launching an application). This PDF document cannot be accepted."
Word Perfect and Word files converted to PDF via Acrobat can cause this behavior when Acrobat is set to "High Quality Print"- often the default. In the distiller settings make sure the Default Setting is set to Standard, not "High Quality Print" or "Press Quality". These settings actually add an attachment to the pdf file. To get to this setting, select the Adobe PDF printer, go to Properties, Adobe PDF Settings tab, Adobe PDF conversion settings, Default Settings.