thank you for reply jurgen,
here the requirement is they have external number range for PR 20000001 to 299999999 & when they create an order in SRM it is using the same external number range( they are saying they are not entering any number and the number increments from the last used as we have in case of internal number range ) & they are asking the same functionality when they create PR with File also. but when i debug the code it is calling FM "NUMBER_GET_NEXT " which we use normally and proposing respective internal number range but the user want external number as they have this functionality in SRM