Running Windows 10 Pro 64-bit (Build 15063)
and DirectX 12.

Downloaded and installed Spore Collection. Installation said it was successful.

Trying to run the program threw the following error:
SporeApp.exe - System Error
The code execution cannot proceed because d3dx9_27.dll was not found. Reinstalling the program may fix this problem.

Reinstalling did not fix the problem.

I read the article: DIRECTX FILE NOT FOUND
(support.gog.com/hc/en-us/articles/213039385)

The instructions (and the info from the linked Microsoft pages) make it appear that I would need to downgrade DirectX on my system from 12 to a lower version.

Is this true, or does d3dx9_27.dll just need to exist on my system?

What will DXSETUP.exe (from the first Microsoft page) and the DirectX web installer (from the second Microsoft page) do to the DirectX installation on my system?

Thanx
eljay

You may need older versions of DirectX installed as well (for games which use dll's from previous versions.

A quick search suggests this package is what you should find and install for that particular dll.
DirectX End-User Runtimes (June 2010) - directx_Jun2010_redist.exe

And to add to your question, they just add additional libraries, in this case for Direct 9. Older games will only run on the version of DirectX that was out at the time. From my understanding, sometimes the web installers will detect DX installed and fail to add the necessary additional older libraries. I've always had better luck adding the specific redistributables such as Jun2010 for example.

Just install the package RWarehall listed. You will need it. DX9 is NOT included with later DX. It will not remove DX12.

Thank you both for the reassurance.

I downloaded the June 2010 DirectX runtime package and ran DXSETUP.exe. It ran successfully.
I downloaded the DirectX Web Installer and ran it and it said a newer or equivalent version of DirectX has been installed already and no installation is necessary.

Running these programs fixed the missing DirecX file error I got initially.

Unfortunately, there is still a problem.

Running SporeApp.exe displays a blank screen for a few seconds and then disappears (meaning the desktop is again visible). I checked Task Manager and the spore process is running, but there is nothing visible. If I click on the Spore icon on the taskbar, the screen goes black again for a second or two and returns to the desktop.

Any thoughts on what this problem might be and how to fix it?

Thanx,
eljay

You probably also need to enable DirectPlay - https://support.gog.com/hc/en-us/articles/115003398269-Error-on-launch-The-application-was-unable-to-start-correctly-0xc0000022-0xc0000022