can't convert .crt file into .der file

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Hello, I followed your READ.md instructions carefully, but after downloading openssl software for windows, I am not able to convert .cert file into .der
Where should I run these commands,
$ openssl x509 -in aaaaaaaaa-certificate.pem.crt.txt -out cert.der -outform DER
$ openssl rsa -in aaaaaaaaaa-private.pem.key -out private.der -outform DER

in cmd or in PowerShell or in openssl?
Please help.