An fdf file is a data file. If you attempt to open it with Reader (XI or a rights enabled form with previous versions), it will search for the pdf that created it and open the pdf with the data filled in. If you attempt to open it and you don't have the pdf (or a copy) that created it you will receive an error message. If you have a pdf with form fields that match the fdf, you can import the form data using this.importAnFDF(). Since it is only happening on your computer could it be that others have the pdf so when then open the fdf it actually opens the pdf and imports the form data (as it should if you have the pdf)? Are you sure it is a pdf file you attempting to download? How are you downloading it?