Custom field

I have a custom field and a custom Theme for my invoices
2 things can I use html to list all customer names in my drop down custom field
and how do I get my custom field to be next to the description column.

No, not if I understand what you are asking. When you build a dropdown list, each line becomes a new option. So the list, with just a return after entering each name:

46%20PM

Becomes this dropdown:

03%20PM

If you are asking if you can have a dropdown list that includes all your customers automatically, the answer is no.

You use a line-item custom field instead of a transaction form custom field. See this Guide: Manager Cloud. While these can be used with custom themes, you do not need a custom theme to use one.

Thank you