I'm trying to copy one custom date field to another when the first one is populated. I set up a workflow rule with a field update, but I'm not sure how to copy the date using a formula.  I tried using the DATE and DATEVALUE functions, but no luck.  

Is there a formula that will copy one custom date field to another? 

Does anyone know how to write a trigger that would copy a value from a custom field to standard field?

I have never coded with apex before, so sorry if my question doesn't make sense.

We have been using a custom picklist to store certain info about our clients, but custom fields are not available for a PDF merge.

Our app exchange partner has suggested that we develop a trigger to copy the value from the custom field to the currently unused

"Industry" standard field, which is available for merge.

I'm trying to copy one custom date field to another when the first one is populated. I set up a workflow rule with a field update, but I'm not sure how to copy the date using a formula.  I tried using the DATE and DATEVALUE functions, but no luck.  

Is there a formula that will copy one custom date field to another?