Parameter Description: The QueryStringField parameter gives you the ability to add Conga Composer parameters into a separate Salesforce formula field, and then reference that custom field in the merge process.
To reference the custom field in the merge process:
Create a custom formula field on the object on which Composer is built
Add Composer parameters to the custom field as a formula, similar to what you do when creating a formula field for Conga Batch
Reference the API Name of the newly created formula field as the value of the QueryStringField parameter in the Composer button URL, as shown above