When extracting a page from a PDF, I lost nearly 1KB of data. What exactly is changing here?

Question

I have a project in which I compile content from scanned documents. Usually I send the scans in packets of 15-50 pages at a time, and extract the pages (using Document > Extract Pages...) into a separate folder for compiling and tagging.
Sometimes, usually when starting a new document folder, I send only the title page. Usually I would simply move this single-page document into the appropriate folder, since extracting would do nothing but copy the entire file anyways.
However, one time out of habit, I extracted 'page 1 of 1' into the folder and found that one of the pages is 5.798MB while the extracted file is 5.797MB. Looking closely at the document there are light visual changes but otherwise nothing that would make me think the resolution or information has been reduced or damaged. Namely:
The original scan has a white border around it while the extracted scan does not. This border is not a pixel border or otherwise a part of the scan; zooming in or out, this border will always exist at 1px thickness.
Pixels in the original scan appear solidly square while it seems the borders are lightly blurred in the extracted. The color and size of the pixels has not changed, the literal boundary between two separate pixels is itself blurred (looking at the document at %3200 zoom).
What is this KB of data that suddenly disappears? And does this have some effect on the quality and content of the document, or is this some sort of visual issue otherwise unrelated to the extracting?
The project I have is archival in nature; while 1KB in a 5.8MB document is negligible, I would like to know where this information is disappearing to, and more importantly, whether this information loss could accumulate as documents are passed around over time.

Answer 1

Looking at the content box now, it just shows
[filename].pdf
     Page 1
          Annotations
          XObject: Image w:[width] h:[height]
all of which seems to contain no properties or additional data. I might be missing something here that would tell me more about the information and content of the file but right now I don't see it.
EDIT: I should also note that the width and height does not change between images despite, say, the additional white border.