Very often I want to add some introductory note to PDFs or images. The best field I could come up with for this was the Spotlight Comment field. For these situations it would be great if the the Comment could be rendered just above the Document!
Why don’t you just add an annotation to the PDF?
And I don’t understand how you’re applying this to images.
What, exactly, do you mean by “just above the document.”?
And “for these situations”, do you mean only when you have a comment that you want just above the document? What about other comments that you, and most other users, don’t want displayed? Many users use the comment field for a variety of data. I’d think it’s an all or nothing feature.
I echo Bluefrog, how are you applying a comment to an image? Intrigued.
Yep, for PDFs that would work, but not for images or webarchives.
I endeavour to create a mock-up to make the feature request clearer.
Here a quick mock-up of a DEVONthink Pro window in Three-pane view. It shows a document with a possible area above the document displaying the Note/Comment:
I think for all uneditable (or only with difficulties editable) formats it would be great to have the Note/Comment for a document shown alongside the document. Even better if the Note was rendered as Markdown! 
Why not just add a column for Spotlight Comments?
Well, this is certainly not the same: having an small field and find there a probably truncated part of a deatield note. Or on the other hand displaying the note where it refers to: the document you look at.
I understand that this is not possible at the moment, but I think it would be a great new feature for all non-editable formats. 
Another good use would be for an editable format, with intentionally very restricted editing: the sheet.
Sheets often need some additional information, like what the whole table is about or what a specific column header means - perfectly explained alongside the document, say, at its top.
I keep some tables as markdown documents, beacuse I really need to show some addtional context information at the top of the table and markdown alows this; however with this I loose the great import, export and editing features of sheets.
I get where you’re coming from, you want some detailed comments about a document to accompany that document.
I think one of the best ways to go—and this is not a replacement for your requests, but a practical workaround—would be to create a separate document that contains the notes or comments that links back to the original document. The original document could have the item link for your notes document in its URL field (or as a link in text somewhere if you can edit the original document).
The issue I see is that showing comments as an overlay or somehow as part of the document will not scale very well. It might work for comments of a certain length but will likely not work well beyond that. Using a separate document means your comments can be of arbitrary and, in theory, unlimited length. in other words, if I understand things correctly, your idea will work for some situations, but would likely break fairly badly for many other situations.
Using a linked document will likely work for a considerably larger number of use cases.
But I totally get your need to see some brief notes about a document! A truly legitimate need but a bit tricky to solve elegantly!
What about implementing it as anoher view alternative? We have already the Best Alternative and the Text Alternative, we could add a WithNotes Alternative.
This could even become a user-managed plugin system where, depending on the (master) document format, different available (QuickLook-style) plugins offer different additional views! But now I’m truly getting carried away…
The WIth Notes Alternative seems like it could reasonably be replaced by having the inspector open and selecting documents to view the comments in the inspector, which automatically shows content for the currently selected document and changes when you select a different document.
It strikes me as being like the floating window version of the feature you are resquestng, based on my (potentially incorrect!!) understanding of your request.
By now I have tried the ”Inspector Open" approach for a few weeks and it sort of works, but is far from perfect:
- The inspector is cluttered with lots of other stuff which is rather distracting when you just want to concentrate on content.
- The comment is shown in a very small font.
But the idea to show the comment in a sepearte window - maybe with a bigger font and possibley even with markdown rendering - got me thinking: This shouldn’t be too difficult to implement and would be fully backwards compatible because this window could easily be hidden.