Windows 7: jpeg image, acrobat professional 8 and windows paint application

yesterday i scanned 4 pages from acrobat professional 8 by benq scanner 5000. the file size was 500kb. then i saved the 4 pages into jpeg format, with each file size of 150-200kb.

then i opened the files in windows paint, and did some basic editing nothing major, when i saved the modified image, the size of 4 jpeg files varied from 500kb to 1.2MB

i dont understand why the file size ballooned so much after simple editing in windows paint

JPEG format is not like text document, where you can correct one letter and size of the document won't change.

In JPEG when you edit even two pixels, whole image will be rebuild and repacked. Your images might have compression factor of 65, but MS Paint has fixed factor somewhere between 75 and 85 (do not quote me on that though).

MS Paint has average default settings for saving JPEG, which are might be good for some pictures, but not for others. For MS Paint settings are fixed, pre-programmed, and you can not change them.

Thus, I would recommend using othe software where you can manually change saving quality factor,
like paint.NET