How can I install Directx9 on Windows 10?

How can I install Directx9: https://www.microsoft.com/en-ph/download/confirmation.aspx?id=34429, I'm running Windows 10 but the setup says:"You must be running win98 etc...."

Had the same problem when i tried to run an older game on Windows-10, it complained about a missing dll d3dx9_41.dll.

You can download the "DirectX end user runtimes" from Microsofts website. The exact version depends on the file which is required by your application, in my case it was directx_mar2009_redist.exe.

To find the correct version i analyzed the error message. If the missing file is for example d3dx9_41.dll, it means that DirectX-9 version 41 is required. The list below shows the available DirextX-9 versions, the version can be found at the third column. This gives you a clue of what to search for, the keywords directx Mar2009 lead me to the microsoft download page.

Feb2005_d3dx9_24_x86.cab
Feb2005_d3dx9_24_x64.cab
Apr2005_d3dx9_25_x64.cab
Apr2005_d3dx9_25_x86.cab
Jun2005_d3dx9_26_x64.cab
Jun2005_d3dx9_26_x86.cab
Aug2005_d3dx9_27_x64.cab
Aug2005_d3dx9_27_x86.cab
Dec2005_d3dx9_28_x64.cab
Dec2005_d3dx9_28_x86.cab
Feb2006_d3dx9_29_x86.cab
Feb2006_d3dx9_29_x64.cab
Apr2006_d3dx9_30_x64.cab
Apr2006_d3dx9_30_x86.cab
OCT2006_d3dx9_31_x64.cab
OCT2006_d3dx9_31_x86.cab
DEC2006_d3dx9_32_x86.cab
DEC2006_d3dx9_32_x64.cab
APR2007_d3dx9_33_x64.cab
APR2007_d3dx9_33_x86.cab
JUN2007_d3dx9_34_x86.cab
JUN2007_d3dx9_34_x64.cab
AUG2007_d3dx9_35_x86.cab
AUG2007_d3dx9_35_x64.cab
Nov2007_d3dx9_36_x86.cab
Nov2007_d3dx9_36_x64.cab
Mar2008_d3dx9_37_x64.cab
Mar2008_d3dx9_37_x86.cab
JUN2008_d3dx9_38_x86.cab
JUN2008_d3dx9_38_x64.cab
Aug2008_d3dx9_39_x64.cab
Aug2008_d3dx9_39_x86.cab
Nov2008_d3dx9_40_x86.cab
Nov2008_d3dx9_40_x64.cab
Mar2009_d3dx9_41_x64.cab
Mar2009_d3dx9_41_x86.cab
Aug2009_d3dx9_42_x86.cab
Aug2009_d3dx9_42_x64.cab
Jun2010_d3dx9_43_x64.cab
Jun2010_d3dx9_43_x86.cab

Maybe it is also possible to just install the latest one from June 2010, i'm not sure if it contains the earlier versions too.

The DirectX built into Windows 10 is compatible with DirectX 9, 10 and 11.
So you shouldn't try to install an older DirectX version manually at all. You can really screw up your Windows installation that way.

Unfortunately, there are a lot of programs (mainly old games) that try to install DirectX by themselves or test for the presence of a certain DirectX version in an incorrect way, which causes them to miss that DirectX is already present.

There is really no good solution to that.
If the installer of the old program is brain dead you can't really cure that.

Sometimes it helps to run the installer in "compatibility mode" for XP-SP3.
In some other cases, you can force the installer to continue anyway and the game will just work despite the errors during the installation.
And sometimes you are just out of luck.

You may have to experiment a little to see what works best in your particular case.