A compression result is easy to judge by its biggest number: the percentage reduction. That is the wrong place to stop.
The better question is whether the result still does its job. An attachment that fits an upload limit but has unreadable figures is not finished. Neither is a document that looks correct but no longer supports a feature the recipient needs.
PDF optimization involves choices. Adobe’s documentation describes controls that can change images, fonts, form fields and other document elements. Those controls solve different problems; they are not interchangeable. Adobe Help: Reduce PDF file size with advanced options
For FileStation, we propose a clearer order of decisions. First, understand the destination: a screen, a printout, a submission portal, or an editable form. Second, identify what must survive. Third, try the least disruptive operation. Only then compare the file size.
This approach does not need a complicated scoring system. Put the original and output side by side. Read the smallest important text. Search for a distinctive phrase when the original has a text layer. Try any links or fields that matter. Keep the original separate.
Our view is that a compression tool should celebrate a usable result, not just a dramatic reduction. Sometimes the right result is a modest saving. Sometimes the honest answer is that the requested target is too small for the document’s purpose.