Internal Number Assignment 
Usage
Internal number assignment means that the system automatically assigns a document number to the document when you create it.
Prerequisites
You can define internal number assignment in Customizing for Document Management under Define document types .
You must make the following settings for internal number assignment:
Type of number assignment
Choose a type that supports internal number assignment, for example BLANK as value (internal or external number assignment)
Enter the internal number range
Enter the program for the number assignment
In the standard system, number assignment is controlled by the MCDOKZNR program.
Activities
Internal number assignment takes place automatically if you make one of the following entries when you create a document:
You do not enter a value for the document number
You enter the special character "*"
When you save the document, the system assigns a consecutive number from the allocated number range.