Retaining Quality of Images While Flattening in Preflight

There is absolutely nothing that is done in the Flatten annotations and Forms Fields profile in Acrobat Preflight that even touches the underlying content on the PDF pages. The objects in the “appearance stream” of the annotations and forms fields are simply moved into the page contents and the annotations and form fields themselves removed. Again, the existing content on the page, whether it is text, vector, or raster graphics is not modified at all.

What could be happening is that if the annotations and/or forms fields have objects with transparency that are overlaying the existing page content, if you have the wrong transparency flattening options set (i.e., not High Quality), then yes, the transparency flattening that now occurs could easily yield lower image quality.

If this is not the case, if you could post a before and after set of PDF files, we would be more than happy to take a look at what is going on. FWIW, I personally use this profile and the underlying fixups on a daily basis and have never experienced any image (or any other) quality loss.

          - Dov

PS:     I am also part of the team responsible for Acrobat Preflight at Adobe and as such take a very strong interest in following up on exactly what is going on in your case.