Files with the .SPD extension contain data connected to custom user dialog windows – SPSS software interface components created by the user. The SPSS software is used for conducting statistical analyses, whereas SPD files allow statisticians to devise their own input forms for custom statistical functions.

SPD files are created with a tool built into the Custom Dialog Builder software which can be found in the program menu. The tool window displays a preview of the created dialog window, as well as an input form for defining its target localization. Before the tool is executed in the SPSS software it must be installed, also using the Custom Dialog Builder app tool menu, specifically the File – Install option.