Purchased and downloaded your certificate from your certificate provider like Godaddy, Digicert, SSL.com etc..
Convert your .crt file to a .cer file
- Locate your downloaded .crt file, and double-click to open it.
- Select the Details tab, and then the Copy to File button.
- Select Next in the Certificate Wizard.
- Select Base-64 encoded X.509(.CER) and then select Next.
- Select Browse, locate where you want to save your .CER file, and type in a name for your certificate.
- Select Next and then Finished.
Copy your certificate files onto the server
- Find the directory on your server where certificate and key files are stored, then upload your intermediate certificate (gd_iis_intermediates.p7b or similar) and primary certificate (.cer file that you just converted) into that folder.
Add a Certificate Snap-in to the Microsoft Management Console (MMC)
- Click on your Start Menu, then click Run.
- In the prompt, type mmc and click OK.
- Click File, then click Add/Remove Snap-in.
- On the new window, click the Add button.
- On the new window, select Certificates and click Add.
- Select Computer account for the snap-in and click Next.
- Click Local computer and click Finish.
- Click Close on the Add Standalone Snap-in window.
- Click OK on the Add/Remove Snap-in window.
Import the Intermediate SSL Certificate
- In the MCC Console, click ▸ to expand Certificates (Local Computer).
- Right click on the Intermediate Certification Authorities folder, hover over All Tasks and click Import.
- On the new window, click Next.
- Click Browse, find your
gd_iis_intermediates.p7b
intermediate certificate file and click Open. - Click Next, verify that the certificate information is proper and click Finish.
- Close the the import was successful notification.
Install your SSL certificate
- Click on your Start Menu, then click Run.
- In the prompt, type inetmgr and click OK to launch the Internet Information Services (IIS) Manager.
- Under the Connections panel on the left, click on your Server Name.
- In the main panel under the IIS section, double click on Server Certificates.
- Under the Actions panel on the right, click Complete Certificate Request.
- On the new window, click … to browse, find your previously uploaded primary certificate file and click Open.
- Add a Friendly name to easily identify this certificate in the future.
- In the certificate store option, select Web Hosting and click OK.
Bind the SSL certificate
- Under the Connections panel on the left, click ▸ to expand the Sites folder.
- Click the Site Name that you plan to install the SSL certificate onto.
- Under the Actions panel on the right, find the Edit Site section and click Bindings.
- On the new window, click Add and fill out the following information:
- Type: select https.
- IP Address: select All Unassigned.
- Port: type in 443.
- Host name: leave this empty.
- SSL Certificate: select your recently installed SSL.
- Click OK to confirm, then Close for the Site Bindings window.
Restart IIS (optional)
- Under the Actions panel on the right, find the Manage Website section and click Restart.
Ref: Manually install an SSL certificate on my IIS 10 server | SSL Certificates – GoDaddy Help CA