"Map Salesforce Product Line Items Fields to Adobe Document Fields"

You will need to use the "Form Field Name" from the product mapping section of the merge mapping you have set up and then put this in the word document as a normal tag i.e. {{formfieldname}} but you will need to add a number at the end to reference the number of the line item

{{formfieldname1}}

{{formfieldname2}}

etc

The main issue with this is that a business presumably sells very different numbers of products to each customer. So if you might sell 100 line items but most clients buy 20 line items then the template will end up with 100 rows 80 of which will remain blank. These templates are not dynamic and add the number of rows that are related to the opportunity. 

One workaround that I have used for a client whose contracts would not have more than 10 rows is create a template for each option 1-10. A custom field on the opportunity rolls up a count of the product lines. Then using an CASE statement in the button that generates the contract insert the correct template ID. I have given an example of that button below:

{! URLFOR('/apex/echosign_dev1__AgreementTemplateProcess', null, [masterId= Opportunity.Id ]) }&templateID={!CASE(Opportunity.Count_Opp_Lines__c,1,relevanttemplateID1,2,relevanttemplateID2,3,relevanttemplateID3,4,relevanttemplateID4,5,relevanttemplateID5,6,relevanttemplateID6,7,relevanttemplateID7,8,relevanttemplateID8,9,relevanttemplateID9,10,relevanttemplateID10,Error)}

This is not the nicest workaround and will mean that any change to a template has to be made 10 times but best I could work out.

Possible enhancement Adobe?