How can I save my working copy of InDesign CS3?

Thanks to all for the input.  Here's how it all played out...

Backed up the failing HD on an external drive using Time Machine.

Replaced old drive with OWC SSD drive.  Not difficult.

Initialized new drive with Disk Utility.

Used Time Machine to install old drive contents to new SSD.

Fired up the old iMac with all apps working fine!  Much faster than old drive as well!

A clone is the best approach to try first.

I have successfully cloned to upgrade/replace drives for an old Macbook Pro (one that I use for other purposes, but which just happens to have older CS apps) without losing activation.

Another approcah is to make sure you have a current Time Machine backup, and if worse comes to worse, reinstall a fresh system on your new drive and use the TM backup to restore to the new drive. I haven't personally done that to know if activations carry over, though.

You might also look at a system maintence software like Cocktail to make sure the symptoms you are experiencing are really with the drive and not the OS. When I make clones, I’ll always run Cocktail first so I’m not cloning a fixable system problem.

https://www.maintain.se/cocktail/

https://bombich.com/

When you say your "ordered a replacement" do you mean a new hard drive or a new iMac. Replacing a hard drive in an iMac is possible but can be difficult if you are not used to dismantiling computers. However, you can run the drive externally if you have a good connection. I would recommend Thunderbolt 2 or faster if your computer supports the connections.

After you clone your hard drive to a new drive as suggested, google "can i activate the creative suite 3". Lots of possible suggestions.

For example:

https://cybermike.id.au/adobe-cs3-activation-error-solved/

https://community.adobe.com/t5/download-install/cs3-cannot-activate-cs3-is-now-dead-and-gone/m-p/10223965

(I have no idea if any of these options will work... but it is worth a try.)

Look at an app like Carbon Copy Cloner, which is capable of making a bootable clone of the startup drive. You could clone the startup to an external drive, test the copy by starting up from the clone, and then clone the copy back to the new drive. The question might be whether the problem are with the drive itself, or is there a problem with the OS?

In short, yes, there is a way past your situation.

You need some additional peripheral hardware, and some specific software. Quickly, before your hard drive dies.

On the hardware side, you need your new HDD/SSD (of course) and a way to connect it to your system without installing/replacing your current drive. If you don't plan to use a home-built external drive in the future, a service tool like this IDE/SATA adapter will serve the task. This device will serve for most any hard drive or 2.5/3.5 cased SSD that's been created in the last 15 years.

On the software side, disk cloning software will help you move the entire existing hard drive to your new HDD/SSD. I strongly recommend SuperDuper. It's a powerful free utility for cloning your existing drive to your new replacement. At minimal additional cost (less than $30US) you can purchase it and get useful addtitional capabilities and support the efforts to create and update this handy utility. This lets you create a useful, bootable copy of your existing system and bypass the need for reinstalling/updating/(and generally) reauthorizing your existing software. For your needs, this will serve dutifully and effectively to move your existing setup to your new drive without reauthorizing your CS3 install.

That's the good news. Now let me share the not so good news.

I think it's safe to assume that you're not only running an old version of InDesign, which was superceded in, like, 2008, but lots of other old software. And an old version of MacOS as well. And replacing a hard drive in an old iMac can be anywhere from difficult to tool-bouncin'/cryin'/cussin' miserable for even experienced technicians.

And depending on how old your system is, finding long-obsoleted service parts to replace your old hard drive will be a big issue. Before you start, you want to research exactly what kind of drive you need for replacement. It may be as easy as getting a part number and picking its replacement from a huge list of vendors and products on Amazon. But it's just as likely that it won't.

This is no minor undertaking. You want to carefully research what you want to accomplish and exactly the resources you need to amass and the work you'll need to do to the job. It's not as easy as slamming a new hard drive into a PC case. And you need to consider whether it's worth the cost to do this yourself or pay through the nose for technicians to do this for you. Because if you do this yourself it's entirely likely that all you'll end up with nothing more than a pile of obsolete parts. I do system repairs for folks with old all-in-one systems like ancient iMacs under considerable duress and all too often considerable expense. Frankly, working on old iMacs is the bane of my existence.

But yes, it can be done. Good luck.

Randy