The date format mm/dd/yy is localized by Excel: even though the file specifies a different format (e.g. dd/mm/yyyy), it will be drawn differently based on system settings. It makes sense when the producer and consumer of files are in the same locale, but that is not always the case over the Internet (like in this case). Unfortunately there is no «smart» way around this yet.
To get a correctly formatted date in the generated PDF file, you can change the placeholder type from Text to Date in PDF Mail Merger.
Select Date as the new placeholder type:
Select the date format you want to use or define your own date format:
You can use the following characters to define your own date format:
|1-12||The month, beginning at 1|
|01-12||The month, 2-digits|
|Jan-Dec||The abbreviated month name|
|January-December||The full month name|
|1-31||The day of the month|
|01-31||The day of the month, 2-digits|
To get a correctly formatted date in the generated PDF file, you can save the date as Text format instead of Date format directly in your Excel spreadsheet. This way the date will always be printed as you can see it in your Excel file.