where is the private.key?

I am trying to follow instruction here - https://developer.adobe.com/document-services/docs/overview/2.2.0/pdf-extract-api/quickstarts/ to test pdf extract, and as indicated below, there should be private.key no matter it is personalized download or non personalized, i tried both and both downloads don't have private.key! where and how should i get it?=================== 

Authentication

Once you complete the Getting Credentials, you will receive a zip file with content whose structure varies based on whether you opted to download personalized code samples. The zip file structures are as follows:

• Personalized Download: The samples download.zip contains a private.key file and an adobe-dc-pdfservices-sdk-python-samples directory. Each sample directory contains the sample code as well as a preconfigured pdfservices-api-credentials.json file.
• Non Personalized Download: The samples download zip contains the private.key file and unconfigured pdfservices-api-credentials.json file.