..sda is a file extension that OpenOffice.org uses (more specifically
OpenOffice Draw). I would assume they saved in that but named their document
"whatever.xls" and the actual extension of ".sda" got tacked onto the end.

"Alan C" wrote:

A client sent me an Excel spreadsheet with password protection. the file is
named "...xls.sda" I cannot open it with Excel or any other program. Any
suggestions?