Acrobat DC Pro will not export to JPEG

Here are a few ideas:

Before you try anything else have you checked if this problem happen only when you try saving to JPEG or does it happrn with when you try saving to any other format?  

Another observation is the jpeg in use or opened in another program when you are trying to save it?

Does changing the filename before commiting the export make any difference?

Have you considered saving the file to MS word and then converting back to PDF would work?

Is the program that you created the original file available? 

And here is what I would try:

1) there is a setting EDIT---->PREFERENCES---->>> Export to PDF.

select the export format from the item list and click the edit button.

See in there if anything have changed. OR, manually modify options and try again

2) uninstall and reinstall Adobe Acribat using the cleaner/repair tool and follow the recommended steps by Adobe. (You can aldo try and uninstall and reinstall the application using the Adobe CC Desktop app.

3) update all licensed siftware in that computer to reflect the current version on each product

4) See also if the security for the files is set too high, loke for example, if the jpeg was created from MS Word see if you can lower the security levelz of the macros (like or uninstall, reinstall visual basic addins and visual basic C++ addins)

5) create a new user account in your Windows 10 without deleting the current one and see if the problem happens with that account

6) try to print the file to PDF instead of using save as or export function

What operating system are you using, and what location in that operating system are you trying to save into?