It is highly recommended that you send each parameter to Subtitle Workshop between " " to avoid problems with spaces in the name/path of the files.

To open a file:
SubtitleWorkshop.exe "/OPEN(File)"

Example:
SubtitleWorkshop.exe "/OPEN(C:\Subtitle.srt)"

To convert from one format to another:
SubtitleWorkshop.exe "/CONVERT(Input_File/Output_File/Output_Format/Input_FPS/Output_FPS)"

Input FPS and Output FPS are only required if you are handling frame based files, if not, you may specify any value. In the FPS, if not a rounded value, the decimal digits have to be separated using the decimal separator (configurable from Control panel/Regional and language settings) of the PC on which Subtitle Workshop is running. Usually it is "," or ".". The subtitle format has to be in the form of a string, and if you are using an updated version of SubtitleAPI you may specify new formats, since the possible formats depends on the version of SubtitleAPI.

For you to know all the supported formats and *exactly* how you should write them, call Subtitle Workshop like this:

SubtitleWorkshop.exe /GetSupportedFormats

After doing this Subtitle Workshop will save a list of the supported formats to the path in which it is installed, in a TXT file with the name "SupportedFormats.txt".

Some examples:
SubtitleWorkshop.exe "/CONVERT(C:\Folder\Sub.smi/C:\Subtitle.pjs/Phoenix Japanimation Society/25/29,97)"
SubtitleWorkshop.exe "/CONVERT(C:\Subtitle.vsf/C:\Subtitle.jss/JACOSub 2.7+/23,976/0)"
SubtitleWorkshop.exe "/CONVERT(C:\Subtitle.srt/C:\Subtitle.sub/MicroDVD/29,97/29,97)"

To delay a file:
SubtitleWorkshop.exe "/DELAY(Input_File/Output_File/Input_FPS/Delay_in_Milliseconds)"

Example:
SubtitleWorkshop.exe "/DELAY(C:\Subtitle.srt/C:\Subtitle.srt/0/-5000)"

The example above will set a -5 seconds delay to Subtitle.srt and overwrite it. We specify 0 as FPS since we are loading a time based format. As in the parameter to convert a file, if FPS is not a rounded value, the decimal digits have to be separated using the decimal separator of the PC in which Subtitle Workshop is running. If you specify a wrong FPS and FPS is really needed, then the default FPS (25) will be used.
