I should note that I am using a Window PC running Windows 10
If your are referring to this page than your are not getting all the necessary info on tethering. Adobe documentation on this page for tethering has become essentially worthless.
Look at this page and you will see support for your camera was dropped after Lightroom 4.1 (this is the legacy link)
Pretty poor documentation for tethering, about as bad as their programming quality control lately.
What a waste of a day!!
Thank you for your help.
I pay for a monthly subscription to the Adobe suite so have automatically got the most up to date version of the software. Do you know if it's possible to choose to install an earlier version that should work with my camera?
Alternatively do you know of a program that will allow me to use my camera via tethered shooting?
Thank you again for your help. I wish I had asked earlier!
You could try the Canon software that came with the camera to see if it will run on Windows 10 and also offer tethering. My Canon 5Dclassic (which is about the same vintage as your camera) had Canon tether support and like your camera was no longer able to tether after Lightroom 4.1. I can tether it using Image Capture on my Mac. The Canon 350D was released 11 years ago so support with other tethering software is probably going to be hard to find.