Why not download the demo, and try it for yourself?

Welcome to the forum. Short answer: Yes, they can be opened from within Finale. 

Please download the 27 demo and check it for yourself. The Aria playback engine and Garritan Instruments for Finale will not be included in the demo but otherwise, the app is fully functional during the demo period.

Mac or Windows and what OS version?

How your files will display and what you need to do will depend on many factors. Please post any issues in this thread and resist the temptation to create new ones for every issue if you have any.

Thanks for your fast replies.

"Why not download the demo, and try it for yourself?"
Because I'm afraid that the demo version will replace mine : if it doesn't work, I'll have nothing left!

"The Aria playback engine and Garritan Instruments for Finale will not be included in the demo"
What is it ?

Windows 10 version 22H2

IIRC the new version should not overwrite the old one. To be extra safe, you may want to wait for one of my fellow users to confirm that.

27 will ask to overwrite earlier versions but I have no idea if that applies to versions older than 25 on a Windows machine. When in doubt, move 2007 to a different directory for awhile.

Your Win machine needs to be operating 64 bit to use Finale 27.

The demo doesn't include the Garritan sounds and Aria player, but it plays back just fine through the built-in SoftSynth.

When in doubt, move 2007 to a different directory for awhile

A software is not limited to its folder but includes DLL's, register entries, ... : if the new version modifies these the old one will not work anymore, it should be reinstalled but I don't have the installation pack anymore.

Your Win machine needs to be operating 64 bit to use Finale 27.

It is.

"The Aria playback engine and Garritan Instruments for Finale will not be included in the demo"
What is it ?
"The demo doesn't include the Garritan sounds and Aria player"

Yes, I understood, I don't know what are Garritan nor Aria.

The 2007 version is good enough for what I'm doing with it, the only reason I want to upgrade is that it's 16 years old; I just want to know if I shouldn't rewrite my hundred scores.

Can I send one to somebody who is using version 27 to try ?

Sure. Send it to me. My email is encoded in my signature, below.

Garritan is a set of additional playback sounds. Aria is the player that you use to access them, in Finale.

27 will ask to overwrite earlier versions ...

It is not a big glaring screen so make sure you read all the questions Finale asks when you are installing the demo or even the full version.  I can say to your concern about the registry files, no version of Finale I have installed has overwritten any of them. The older version always worked as they always have. And I have updated every time there has been a new version come out.

I just tried a 2004 file and 27.3 opened if just fine. I am in the process of committing all my music to hard copy so I have been opening some very old Finale files. One problem is if you don't have the font installed on your computer that you used in an older version it may not turn out well.

Following your messages I installed version 27: the 2 coexist and work on my PC.
Finale 27 opens old 2007 .MUS files and renames them to .MUSX without touching the old file.
So I'll be able to try version 27 and decide if I buy it or not.

Thank you

Good deal I am sure you will like 27.3. It is all I have now as I have removed all my older versions.