I've tried to do a search myself for this and it's definitely a conflict between something in the older software and the newer OS. You are talking about things that were manufactured 6 years apart. In computer terms it's a long time. Unfortunately, this isn't as simple as putting newer tires on an older car. It's probably closer to putting together a Model T Ford engine with parts manufactured by Tesla.
If you just need DW for a short while, you can purchase just a month for $20. Then you can just turn off and on your subscription as needed when you have small jobs that may come up. Or if you just need to make code changes and are comfortable with code, brackets is a good solution ( Brackets - A modern, open source code editor that understands web design. ). Otherwise, as a paid alternative there is always Coda ( Coda ).
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Adobe no longer supports any of the Creative Suite software. Their phone support will normally shunt you off to the forums right away if you call in with a CS6 or lower issue.
The legacy Creative Suite installers don't run correctly under the latest Mac OS, but you can still run them.
You should be able to follow the info here to get up and running: Installing Creative Suite on macOS 10.12 (Sierra)
Modern Macs do not support the old Creative Suite installers. You must use the terminal workaround described at the link in Jon's answer.
That said, Sierra and High Sierra are not certified compatible with CS5. Good luck.
Thank you for your comments and the comments of Nancy and Ben. I'm not a neophyte but neither am I an expert.
I clicked the link you provided and followed the instructions. IT WORKED. DW installed and functioning as it did before I installed the 2017-001 update.
All this effort because the update froze my Mac. You would have thought the "Chat" help people could have told me the installer would not work with High Sierra after the update. Instead they wasted a couple hours of my time and in the process demonstrated they didn't have a clue what they were doing. In my eyes they looked stupid and made Adobe look stupid as well.
Again, thank you to those that offered advice. Next time I will look to a forum before trying to get help from uniformed chat people.