Drop-down Date field works for me, but not those I email it to

Hi, I have a set of tickets with two drop-downs. One is a text selection, the other is the date. The people I'm sending the form to aren't able to see the date drop-down. They're using adobe acrobat pro. Any suggestions?

I don't have any character limits on the field, and no security measures saved.

Hope someone can help! thank you.