You can use a Salesforce formula field (in this example a CASE function) to determine which template is used in the merge process. The CASE function will evaluate some field - for example, Opportunity Stage - and based on the value of that field will return the appropriate template ID. This template ID is then passed to the TemplateId parameter in the Conga Composer button/link URL to select the appropriate template.
Start by building a formula field (text output) on your master object. Use the Advanced Formula tab to insert the CASE function. A Case statement is an extended “If” statement where the “expression” indicates what field you want to evaluate, the “value” is a potential value of that field, and the “result” is the result you want when that field equals the “value”.
CASE( expression, value1, result1, value2, result2, ...,else_ result)
Modify your Case statement to evaluate the desired field and return the appropriate results In the example below, we evaluate the Opportunity Stage field and return various template IDs accordingly. After the last value and correlating result, we’ve entered “” as our “else result, ” which will populate if none of the other conditions are true.
"Value Proposition", "a008000000CZNDh " ,
"Proposal/Price Quote", "a008000000DiYKJ",
Note: This formula field can be added on the page layout or not; either way it will always be evaluated and populated, as long as the field-level security is set to "visible" for any user profiles using Conga. Although for template development purposes it may be handy to have it on the page layout to begin with. Also, if you want users to be able to see the else_result you’ll want the field added to the page layout. Finally, users on Professional Edition of Salesforce will have to add the field to the page layout, as field-level security is not an option.
Add this custom formula field into your Conga Composer button URL as part of the TemplateId parameter.
Conga Composer will now look to the value of your Case statement formula field to see which template ID is designated and will then pre-select that template in the Conga Composer dialog box.