Enter the transaction OAOR or Option "Find"  from the SAP menu

Press Enter 

Fill Class Name and Class Type always  with the values shown below:

• Class Name: BUS2072
• Class Type: B0

And press 

Fill the concerned Controlling Area and Document number  

Press Enter 

Select the folder : Cost Accounting Document

And after choose folder: Document types for obj

Choose the document type according to the extension of the file you want to attach

Double-click on 3S-xls documents if you want to attach xls document

and select the file that you want to attach to the posting with a double click

Additional attributes of the attachment :

You can fill Description and up to 5 keywords

After that, the document is stored (archived).