I've tried to use the SET SPACES parameter but it doesn't seem to make any difference. I would like to minimize the space between columns in pdf output.

Here is the method we use (assuming four columns in the report):

ON TABLE PCHOLD FORMAT PDF
ON TABLE SET HTMLCSS ON
ON TABLE SET STYLE *
UNITS=IN,PAGESIZE='Letter',LEFTMARGIN=0.25,RIGHTMARGIN=0.25,TOPMARGIN=0.25,BOTTOMMARGIN=0.00,SQUEEZE=ON,ORIENTATION=PORTRAIT,$

TYPE=REPORT,FONT='ARIAL',SIZE=8,COLOR='BLACK',BACKCOLOR='NONE',STYLE=NORMAL,RIGHTGAP=0.00,LEFTGAP=0.00,$
TYPE=REPORT,COLUMN=P1,SQUEEZE=1.50,$
TYPE=REPORT,COLUMN=P2,SQUEEZE=5.00,$
TYPE=REPORT,COLUMN=P3,SQUEEZE=0.75,$
TYPE=REPORT,COLUMN=P4,SQUEEZE=0.75,$

Thanks for your help. Adjusting the GAP did the trick!

Glad to hear it. Just don't try it with HTML