Recently, I had to enable CDN for our Sitecore instances. After following the instructions available in Sitecore documentation, everything seemed to work fine.

There was use case where we had to exclude PDF documents from the CDN route to keep the security for some of the documents in place. The suggested approach was to add a processor in the getMediaUrlOptions pipeline.

So I create a below processor:

using Sitecore;
using Sitecore.Diagnostics;
using Sitecore.Pipelines.GetMediaUrlOptions;
using Sitecore.Pipelines.GetMediaUrlOptions.Processors;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Foundation.Core.Pipelines.MediaLinks
{
    public class MediaLinksProcessor : GetMediaUrlOptionsProcessor
    {
        public override void Process(GetMediaUrlOptionsArgs args)
        {
            Assert.ArgumentNotNull((object)args, nameof(args));

            if (!args.MediaItem.Extension.ToLowerInvariant().Contains("pdf"))
            {
                return;
            }

            args.MediaUrlBuilderOptions.AlwaysIncludeServerUrl = false;
        }
    }
} 

And added a config file to patch the processor:

<?xml version="1.0" encoding="utf-8"?>
<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/">
	<sitecore>
		<pipelines>
			<getMediaUrlOptions>
				<processor type="Foundation.Core.Pipelines.MediaLinks.MediaLinksProcessor, Foundation.Core" patch:after="processor[@type='Sitecore.Pipelines.GetMediaUrlOptions.Processors.SiteModeProcessor, Sitecore.Kernel']" />
			</getMediaUrlOptions>
		</pipelines>
	</sitecore>
</configuration>

After adding this processor, the pdf files were excluded from the CDN Urls and we got the expected results.

The reference I liked is listed below:
https://maciejz.dev/cdn-url-in-sitecore-shell/

Hope this helps for someone looking for the similar use case.

Thank you.. Keep Learning.. Keep Sitecoring.. 🙂