Specify an HTML document as the original and convert to a PPT format by setting /C switch to 001. On-screen confirmation with the /V switch.
ConvertPPT /S "C:\HTML\sample0003.htm" /T "C:\PPTOutput\s0003.ppt /C001 /V
Note it is highly encouraged that you use the Verbose (/V) switch initially to see what the status of your conversion is.