Hi Mohan,
PDMToday() without any parameters gives you the time when you run PDMToday
PDMToday(-1) Beginning of day, today
PDMToday(1) End of day, today
PDMMonth() gives current Month number, example 4 for April
PDMMonth(PDMAddMonths(-1)) gives previous Month number, example 3 for March
More information about pdm functions is covered in the 14.1 wiki page, https://wiki.ca.com/display/CASM1401/WriteCABusinessIntelligenceReports#WriteCABusinessIntelligenceReports-PDMFunctions
From what I know, base function behavior of PDMFunctions has not changed since SDM 12.6/12.7/12.9
_R