Files with es3 file extension seems to be nowadays mostly found as special digital signed documents prepared using the Hungarian e-Szigno software.
There is one other file type using
the ES3 file extension!
.es3 - Canon VIXIA HG21 high resolution exported movie
ES3 file extension - e-Szigno signed document
What is es3 file? How to open es3 files?
File type specification:
The es3 file extension is associated with the e-Szingo, Hungarian on-line service, which allows users to create digital signs and digital certificates.
It looks like es3 file contains digitally signed document from e-Szingo.
This es3 file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.