Formatting numbers in text box using Mail Merge

[Rozza]

I am trying to generate numbered tickets using mail merge with the recipient document an excel sheet with the numbers on and the master documet a Word doc.
I format the numbers on the excel sheet to my preferred format i.e. "0000123" by using Custom for the required format.


However, when I merge the Word letter document and the Excel number sheet, the numbers in my text boxes on the letter documet have reverted to e.g. "123" i.e.
dropping the leading zeros.
Anyone know how I can maintain my preferred format in these circumstances?
Or an alternative way of generating sequentially numbered documents without coding?