Thanks Eric. What is curious and unexpected to me is that there is a similar allowed extensions config variable (in that same config file) for FILES and that one *does* include 'pdf'. In addition, a glance through the js file for the fck editor (fckconfig.js) shows this -
FCKConfig.LinkUploadAllowedExtensions = ".(7z|aiff|asf|avi|bmp|csv|doc|fla|flv|gif|gz|gzip|jpeg|jpg|mid|mov|mp3|mp4|mpc|mpeg|mpg|ods|odt|pdf|png|ppt|pxd|qt|ram|rar|rm|rmi|rmvb|rtf|sdc|sitd|swf|sxc|sxw|tar|tgz|tif|tiff|txt|vsd|wav|wma|wmv|xls|xml|zip)$" ; // empty for all
Note the presence of "pdf" in that list as well. At any rate, your suggestion does seem to work. I suggest that you add a KB entry about this unusual requirement.