I have used this program for Sales Order upload. it is a direct input program. it takes data in a fixed format file and updates the SAP tables.
if you want to use this you will have to format your data in the required format. if your source system is also SAP, you can use program RVINVBT0 to extract data. then you won't need to format it manually. if source system is not SAP, then you can check the format of the file RVINVBT0 is generating and format your legacy data in same format.
Then, on target system then you will have to run RVINVBT0 and upload file.
Try this and let me know if you need more detail.
I think you can use this program for upload. Is your source system a SAP system. if that is the case try running RVINVBT0 and extracting one document from source system. it will create a file. then run RVINVB10 on target system and upload that file.
then see in VA43( in target system) whether that contract is moved or not.