In MS Word we have mail merge option, for which we can select the data source.
When i select the datasource as one of the worsheet in an excel, the main
document refers only the same worksheet for all its datasource.
But if one of the sections in the main document wants to refer to other
worksheet in the excel file, the previous referenced fileds are lost. Hence
the option should be given to select across the worksheets for atleast a
single excel file.