I would like to upgrade my Debian machine from Jessie to Stretch, but aptitude is reporting that I have 19 obsolete packages. Some of these, like BerkeleyDB, I use routinely.

A [set of upgrade instructions](https://linuxconfig.org/how-to-upgrade-debian-8-jessie-to-debian-9-stretch) say to remove any obsolete software before doing the upgrade, but I want to continue using some of the software. Am I stuck using Jessie forever?