IE can have issues downloading the CRT file appropriately; at times it will change the extension of the .CRT file to _CRT. Simply renaming the downloaded file extension will correct the issue. Testing this link via Chrome is recommended.
If the browser is able to download the CRT file correctly, you may see this warning shown below. Select "Keep" to allow the file to be downloaded.
3. Once the downloads have completed, install certificates by double-clicking the files. When prompted to OPEN the file, select the "Open" Button.
4. The certificate dialog appears. Select the "Install Certificate..." button at the bottom.
5. The Welcome to the Certificate Import Wizard dialog appears. Select the "Next" button.