Can't change my PDF Export settings

Does this help?

https://helpx.adobe.com/indesign/kb/indesign-tools-panels-dont-respond.html

No it does not help

Since @Simulacrum reported having this problem more recently than the original post, I'll go ahead and leave this here. Maybe it will help other people searching for answers as well.

I just encountered the same bug here. None of the drop-down menus in my Export dialog were accepting any changes. The solution that worked for me was to reset InDesign's preferences.

In CC, you can do this by quitting the application and then relaunching it while QUICKLY pressing control + command + shift + option all at once. If you press all four keys as soon as InDesign begins to launch, you should see a dialog box saying "Startup Alert: Delete InDesign Preference files?" Click "Yes," and you'll hopefully have an InDesign that behaves correctly. Good luck.

P.S. You do have to be very quick on the draw. If you don't get the dialog box, just quit and try again.

I, for one, would like to see Adobe change away from this 3- or 4-key reset click. It should be simplified to some sort of reset button in preferences, maybe. Don't know why, but on some computers, I have had to try to reset with this keyboard shortcut, and I have tried over and over again, while InDesign doesn't see the reset shortcut, and I wait for it to load and shut down over and over. I wish there was just simply a button to click in preferences when I want to blow prefs!

I totally agree!

But I just discovered this a short time ago. The current version of Photoshop CC 2017 already has this. Look at this screen capture:

Hi Steve,

Yeah, when I saw that in Photoshop, it got me to wanting the same thing in InDesign!

I'm experiencing the same issue. Resetting preferences or just relaunching ID is only a temporary fix, the issue returns when ID is open for a while.