The Export PDF function seems to be very temperamental and does not seem to expand/open with the first PDF file I open.
Only when I have opened a 2nd file does it expand and allow me to convert documents into Word etc.
Currently it is not even expanding for any number of PDFs I open despite being on the Export PDF plan.
Please try once to repair the application installation and also check if the application is updated to the latest patch released.
Launch the application and go to help menu > Repair Installation and Check for updates.
If the issue still persists, please provide some more information on this.
What exactly happens when you try to export PDF? Do you get any error message?
Also, please try to export PDF online here: https://cloud.acrobat.com/exportpdf
Check if you can export PDF without any issue.
Let us know how it goes.
My version is Adobe Acrobat Pro XI running on Win 7. I have a similar problem, except it is the "save file as image" that does not work. The other "Save as" work. It used to work a few months ago. I have turned off RBG in the colour management section as advised and changed the colorspace to color RBG. I also repaired the Abobe Installation to no avail. Checking for Updates returned a message stating no updates available. The only thing that can try is to desinstall and reinstall.