A family of Microsoft word processing software products for creating web, email, and print documents.
Neither the AI answer nor Lin's answer recognizes that when you print on the backs of the badges, each row of data in the source of page 2 needs to be reversed from those on the first page. For example, if the first row of page 1 contained items 1, 2, and 3, then the first row of page 2 must be items 3, 2, and 1.
There is nothing in Word's mail merge that can automate this. Instead, you need to split your data source file into two files. The first file should contain only the data for the fronts of the badges, in the original order. The second file should contain only the data for the backs of the badges, with the data for each row of badges in reverse order compared to the first file.
Print the fronts of all the badges from the first data source, using only the merge fields for the data on the badge fronts.
Then put the badges into the input tray again, oriented so the next print run will print on the backs of the badges. If your printer will start the run by loading the last-printed sheet first, you need to re-sort the sheets so the first-printed sheet will be loaded first (alternatively, you could change the order of records in the second data file to print the pages in reverse order, but that process is error-prone).
Finally, run the mail merge with the second data file,. It should contain the <Next Record> fields in the same places as for the first run, and only the merge fields for the data on the badge backs.