Replacing a few pages in my PDF made the file size suspiciously small

[Panimal]

Hello!

I recently revised a 400 page print document by replacing 7 pages in the PDF and it made the file size suspiciously smaller!

The original was exported to PDF from a book file composed of 61 InDesign files (184mb).

The revision was a more round about way- opening and exporting 6 individual InDesign files to the proper output settings and replacing the 7 single pages in the PDF and saving as a new version number (108mb).

The reason for the round about way of editing the draft is because all the files are stored on a server and it's easier to make the simple changes while working from a remote location.

Any idea what is causing the file size to be much smaller?

Thanks for taking the time!!

[Test Screen Name · Accepted solution]

Probably you saved as a new name (SAVE AS) and before you used SAVE. Save leaves wasted space ,save as reclaims it.

[Panimal]

WOW! I've never noticed this happening before! Thanks so much for the refreshing insight!

Can you explain or direct me to a resource so I can understand this: "Save leaves wasted space, save as reclaims it."

Thanks again!!