Change PDF file size

A form wants a number, so give it a number

Court filing portals, job application forms, visa systems and university upload pages all cap the file size, and they refuse the upload without telling you how far over you are. A slider marked medium is no help against that. You need the output to land under a specific count of bytes.

The compress tool takes the number directly. Type 500 in the KB box, or switch the unit to MB and type 1. The unit switch treats 1 MB as 1,024 KB, so a 1 MB target is 1,048,576 bytes.

Watch out for the other kilobyte. Some upload forms count 1 KB as a flat 1,000 bytes, which makes their cap 2.4% tighter than the same number here. If a file that looks correct still gets rejected, drop the target by 3% and run it again. The extra cut is invisible on the page.

The size buttons hide themselves for a reason

The tool never offers a target that is larger than the file you gave it. Load a 300 KB document and the 500 KB and 1 MB buttons disappear, because compressing to a size the file already beats is a no-op that would waste your time and tell you nothing.

This also means the tool cannot make a PDF bigger. Nothing here pads a file with filler bytes to satisfy a minimum size rule. If a form demands a floor rather than a ceiling, the fix is better source material, usually a higher scan resolution, not a compression tool.

What happens when the number is out of reach

Four methods race for your target. If one of them gets under it, you get that file. If none of them does, you still get a file: the smallest candidate that passed verification, along with the size it actually reached. Nothing is silently shipped and nothing is silently given up on.

The gap tells you what to do next. A file that lands at 1.2 MB against a 1 MB target is close, and dropping two pages of photography usually closes it. A file that lands at 4 MB against the same target has a different problem, and no setting on this page fixes it.

Which number to ask for

Which number to type depends on what the receiving system actually asked for.

• A hard cap. Use it exactly. Choosing 100 KB when the form allows 2 MB throws away quality for nothing.
• A guideline. Pick the largest size that still clears it, because every KB you leave unused is detail you keep on the page.
• No rule at all. Do not type a number. Run the tool with no target and the lossless methods do the work: the document gets rebuilt and its embedded fonts get subsetted, which changes no pixels and no characters.

Then check the size the receiving system reports back, not the size your file manager shows. Mail systems encode attachments, which adds about a third to the transmitted size. A 1 MB PDF can arrive as a 1.37 MB attachment and trip a limit the PDF itself never came near.

How often a given number is reachable

The public bench ran four targets, 100 KB, 200 KB, 500 KB and 1000 KB, across 120 cases, and met 55 of them. By target: 100 KB on 23 of 56 cases, 200 KB on 18 of 38, 500 KB on 9 of 16 and 1000 KB on 5 of 10.

Those are the only four numbers with a measured reach behind them. Every other size a form might name, 50 KB, 300 KB, 2 MB and the rest, has no bench figure, and any page that quotes one for those sizes made it up. What holds for all of them is the direction: the smaller the target, the more it depends on your document being a scan rather than typed text.

The general compression guide covers what is making your file heavy in the first place, which is the part that decides whether the number is reachable at all. The compress hub lists the rest.