Hello Geralde,
As per the description above, you are not able to activate the Acrobat Pro 9 license on your Windows 10 machine, Is that correct?
The record shows that the license of Acrobat Pro 9 is a part of the Volume license of Adobe Design Standard CS 5 which is registered with your Adobe ID.
In order to activate Acrobat Pro 9 on your machine, you have to download and install the Adobe Design Standard CS5 and choose custom installation and choose Acrobat only and complete the installation. Then use the serial key for activation.
To download the setup of CS5, please log in on Adobe's licensing website https://licensing2.adobe.com with your current Adobe ID and password and download the setup. You may also refer to Adobe Licensing Website | Serial numbers, orders, and accounts
Note: Acrobat 9/CS5 is already declared as End os support product, and Acrobat 9 is never tested on Windows 10, so above suggestions may or may not work on Windows 10, for more information, you can refer to End of support | Reader 9 and Acrobat 9 (and earlier)
For CS 5 Adobe Support Policies: Supported Product Versions
You may also refer to Error: "The serial number is not valid for this product" | Adobe Creative Suite
Feel free to update this discussion in case you need further assistance.
Regards,
Anand Sri.