If you have more than one field you would like to evaluate upon using the filter parameter, please see use cases below on how to achieve this.

1) Create a formula field that will evaluate the logic that you will need (this will allow more flexibility by using formulas). Use whatever value that is displayed in the formula that evaluates as true to be the field that is used in your filter parameter.

Ex: if the formula field equals true1, then this should bring in your first DocGen Package
filter field = true1
button = &filter={!Object.formulafield__c}

2) If formula fields do not work for you and you would need to have the DocGen Package appear when you need your field criteria to exactly match, you would need to have the value added to the filter field without any spaces in between

Ex:
filter field = Closed WonNew Customer
button = {!Opportunity.StageName}{!Opportunity.Type}