This article describes what a CSR file is, how to open it, and what options you have to convert this file to another certificate format.
18. Generate a CSR and install an SSL certificate on IIS 10 from the internal CA
A file with the CSR file extension is a certificate signing request file used by websites to verify their identity with a certificate authority.
These files are partially encrypted, with the encrypted portion describing the domain, email address, and country/state of the requester. The public key is also included in the file. The CSR file is created using both the public key and the private key, the latter of which is for signing the file.
Some CSR files can be opened with OpenSSL or Microsoft IIS.