Surfer does not require you to unzip the files from the SDTS.TAR.GZ file first. You can:

1. Simply select a command that prompts you for a grid file (e.g. Home | New Map | Contour).
2. In the Open Grid dialog, change the Files of type to DDF SDTS DEM.
3. Select the SDTS.TAR.GZ file and click Open.

In Surfer 10 and previous, it was necessary to unzip the data first to your hard drive to use it in Surfer.

1. Unzip the data using a program like WinZip or similar
   1. Note:  If you are using WinZip, click Options | Configuration, click the Miscellaneous tab and in the Other category, un-check 'TAR file smart CR/LF conversion' in order to properly unzip the files.
2. When you unzip the file (for example, 3809474.DEM.SDTS.TAR), there will be many [.DDF] files that are contained in the SDTS transfer. All these files must be together in the same folder.
3. In Surfer, select a command that prompts you for a grid file (ie. Map | New | Contour Map).
4. In the Open Grid dialog, select any one of the DDF files and click Open.

Updated October 25, 2018