Not possible with the current PDF Explorer public release, but the script functionality of the
PDF-ShellTools, v3.1 and up (that will be also available in the next PDFE version), has access to the PDF annotations, so a script can be used to create such functionality.
I've duplicated this forum topic in the PDF-ShellTools section of the forum and have
posted there a sample script that dump to a CSV file all the PDF annotations found in each PDF.
That same script will work with the next PDF Explorer, higher than the actual 1.5.66.2, version release.