This error is displayed by WordPress when uploading PDC files because WordPress only accepts uploading of certain known file types through its Media center. WordPress may also display the error message “Sorry, this file type is not permitted for security reasons.”
If you want to upload files to WordPress you must use an FTP program.
Once you have connected via FTP, create a sub-folder in the /html folder – for example PDCFiles. Then upload your PDC files to this folder.
The link to a specific PDC file would then be for example http://www.domainname.com/PDCFiles/myfile.pdc.