File Extensions

 I need the ability to upload .cdr files which are corel draw..I input the file extension and it will save once and then when I re-open the extensions tab the cdr is no longer there. How can I get the extension to stay as it is an absolut emust for me as these are the only file we use for screen printing...

Please avoid the "dot" , simply  enter cdr (if you are to use more than one extension, it goes comma separted)