The file extension filter can permit all files, restrict specific extensions or only permit specific extensions. If you want to specify the file types Web Users can or cannot upload, type each file extension in this box. Type all extensions without periods (.), separate them with commas, and do not add line breaks or spaces. For example, if you want to allow only .txt, .xls, .xlsx, and .csv files, type txt,xls,xlsx,csv. The maximum number of characters for this field is 2000.