SDA files are in most cases drawings from very old version of OpenOffice, back then called StarOffice, with the .sda files being last used in version 5 of the software from 1998.
As you see, these files are pretty old, yet some can be found on old computers and often users want to convert these to some generic raster format, even the standard bitmap BMP format.
Some versions of the successor OpenOffice/LibreOffice Draw tools might still support .sda files and these are your best option how to handle sda to bmp conversion. You can find installation packages for old software on abandonware websites, you might be able to find old StarOffice as well, for example in the WinWorld library.
Updated: November 2, 2023