Quick answer
That is different from the more common maximum-size rule. If a form says less than 100KB, under 100KB, or maximum 100KB, the file must be smaller. If it says greater than 100KB or minimum 100KB, the file must be larger than that minimum.
This wording appears on forms that want a readable scan, a clear photo, or a document with enough detail. A very tiny image may be rejected because it looks blurry, pixelated, or incomplete even though the file is technically small.
What usually works best
The safest move is to read the exact instruction twice. If the form gives both a minimum and maximum, such as greater than 100KB and less than 2MB, your file needs to land between those two numbers.
ExactSizer is mainly useful when the file is over a maximum limit and needs to be compressed. If your file is below a minimum limit, avoid compressing it further. Instead, export the original at a higher quality, use larger dimensions, or scan the document again with a clearer setting.
If it still fails
If the instruction is confusing, try to identify the range: minimum size, maximum size, accepted format, and pixel dimensions. Most upload failures come from one of those rules, and checking them in that order usually saves the most time.