Only Webmasters and above can do this.
When uploading files and images in the content editor, we only allow specific file extensions to be uploaded for security reasons.
If you need to share file types other than those listed below, we recommend using a file-sharing service such as Dropbox or Google Drive.
Supported File Types:
.CSV
.DOC
.DOCX
.MP3
.PDF
.PPT
.PPTX
.TXT
.WAV
.XLS
.XLSX
.ZIP
Supported Image Types:
NOTE: Only image file types can be uploaded to the Images folder.
.BMP
.GIF
.JPEG
.JPG
.PNG
.TIFF