Only Webmasters and above can do this.

When uploading files and images in the content editor using CKFinder, we only allow certain file extensions to be uploaded for security reasons. They are:

Files: csv, doc, docx, mp3, pdf, ppt, pptx, txt, wav, xls, xlsx, zip.

Images: bmp, gif, jpeg, jpg, png, tiff.
Note that we only allow image file types to be uploaded into the Images folder.

If you have a need to share files other than the file types above, we recommend using a file sharing service such as Dropbox or Google Drive.