Slightly tangential, but Markdown does actually "kinda" support comments with a little bit of abuse of the link syntax. Almost every renderer will swallow the comment in the following example:<p><pre><code> > This is a quote of some kind
[//]: # (This won't be in the rendered output.)
Blah blah blah
</code></pre>
Keypoints brings a lot of other things to the table than just comments, including an upcoming possibility of crosslinking between PDF docs [0], but I've wanted to add annotations often enough to small Markdown documents enough that I've memorised the above little trick. It even works with the original Markdown.pl implementation.<p>[0] <a href="https://keypoints.app/forums/viewtopic.php?f=2&p=788" rel="nofollow">https://keypoints.app/forums/viewtopic.php?f=2&p=788</a>
I am interested to see how this compares to <a href="https://highlightsapp.net/" rel="nofollow">https://highlightsapp.net/</a> but it looks neat, especially if it starts at a place of integration with other platforms.
Devonthink does PDF annotation quite good. The annotation can be markdown or RTF.<p>It’s a whole database system so it might be a little heavy weight for just annotation.
Mac only I think.