File size differential of exact same PDF file

[Lysa5FFD]

Calling all you blue flame thinkers! I'm baffled by this size discrepancy. I'm scanning archives and the situation happens with every single pdf I scan. Method: I scan the document and save it to file as a PDF. The original file was 83.1 MB; when I uploaded it to (https://acrobat.adobe.com/link/home/) "Compress A File" the upload shows as 79 MB on the Adobe site; when it finishes compressing (using best resolution, larger file size - estimated file size after compression is 26.9 MB) When I download the compressed file it's 15 MB! I'm working with thousands of documents and this is impacting decisions about my workflow. I'm on a Mac Mini M1 chip, MacOS 14.2.1 (23C71) Sonoma, and I'm using the Creative Cloud which says that my Adobe version is up to date. Any ideas? 

[try67]

What's the issue, then? That the estimate is not the same as the actual result? It's just an estimate. As long as the quality of the file is good, what does it matter?

[Lysa5FFD]

Good question, @try67 . It makes a difference when I'm choosing which level of compression I choose: High, Medium, or Low. It's basically a storage issue - I'm using a 2TB SSD and it's rapidly filling up. Because I don't have a clear picture of what the file size will be it's a struggle to choose which level of compression I should choose as well as forecast additional storage purchases. If I understand what the metrics are, I can make effective and efficient decisions for this project.

[Lysa5FFD]

Here's another example. I have a 6-page scan of a yearbook. When I try to compress this document (372.9MB!!) online (https://acrobat.adobe.com/link/home/) I get an error message saying that the file size is too large so I have to compress each page individually and then combine them. That is a very time-consuming effort. However, when I do it that way, I end up with a 6.9 MB file size at medium compression. I've attached before and after screenshots. 

[Lysa5FFD]

"I've attached before and after screenshots..." of a single-page example.