BIND 9.9.0 introduced inline signing. BIND writes its backup signed zone file in raw format (this is the format in which the zone data is stored in working memory - it is faster to load/write the zone data in this format).
Use named-checkzone to read the file contents in the format that you're more used to seeing:
named-checkzone -D -f raw myzone.net myzone.net.db.signed
In the above example:
- myzone.net is the name of the zone
- myzone.net.db is the zone master file
- myzone.net.db.signed is the preserved copy of the inline-signed zone