Adding Merge Codes To A Letter
Go to Tools>Letter & Stationery Templates>
Click on the letter to be edited
To insert merge codes press "#" on the keyboard and then search for the code you want by typing any part of the code.
There is a complete list of merge codes in this related article - List of Merge Codes For Alto Letters.
Select the merge code and it will be inserted into the template.
Note: Some merge codes will only work on certain documents. if you create a document which appears blank it may have merge codes that are not for that template. When creating the document it will also warn you if information is missing (for example, if the letter requires an address and the contact has no address).