How to Compress a PDF to a Specific File Size (Under 2, 5, 10, 25 or 100 MB)
The situation
A portal says maximum file size: 10 MB. Your PDF is 38 MB. You press Compress on the first tool you find and get 29 MB — still over. You press Strong and get 9.4 MB, but the small print is now mush.
Compression did not fail. The tool gave you a slider when you needed a number.
This guide is about hitting a number: 2 MB for a job application portal, 10 MB for a school upload, 25 MB for email, 100 MB for a filing system. The method is the same at every size.
What actually decides a PDF's size
Three things, in order of how much they usually matter:
- Images. Resolution (pixels per inch), physical size on the page, and how they are compressed. A scanned page is an image. One 300 dpi color scan of a letter-size page is roughly 8 million pixels; stored as a good-quality JPEG that is 0.5–3 MB per page.
- Fonts. A fully embedded font can be a few hundred KB; a fully embedded Korean, Japanese or Chinese font can be several MB. Subsetting (embedding only the characters used) is the fix, and most exporters do it — unless a setting turned it off.
- Structure. Uncompressed streams, embedded attachments, thumbnails, revision history from "Save" instead of "Save As", and duplicate copies of the same logo on every page.
Text itself is almost free. A 200-page text-only PDF from Word is typically 1–3 MB. If a text PDF is 40 MB, the weight is in images or fonts, not words.
Why one-button compression misses the target
A preset applies one fixed recipe: images downsampled to 150 dpi, JPEG quality 75, done. The recipe does not know your limit. It produces whatever size it produces.
Target-size compression works backwards. It measures what is in the file, estimates what each setting would produce, and picks the strongest setting that still lands under your limit. The output is "9.6 MB, text legible", not "somewhere between 6 and 30 MB".
That is the job PDF300 was built for: you type the limit, it chooses the settings.
Checklist before you compress
- Know the exact limit, and whether it applies per file or per submission (many e-filing systems have both).
- Decide what has to survive: readable text is nearly always required; photo quality often is not.
- Check whether the pages are text or scans. Zoom to 400%. If the letters get blocky, they are scans.
- Keep the original. Never compress the only copy.
- Find out whether splitting into two files is allowed. Two legible files beat one unreadable one.
Step by step
- Set the target 5% under the limit. For a 10 MB cap, aim for 9.5 MB. Some systems count 1 MB as 1,048,576 bytes, some as 1,000,000, and some measure the encoded upload. A margin removes the guesswork.
- Run a target-size compression. In PDF300, upload the PDF, enter the target, download the result. If you are using a preset-based tool instead, start with its middle setting and work down.
- Check the result properly. Confirm the file size on disk. Open the first, middle and last pages at 200% zoom. Read the smallest numbers you can find — table footnotes, drawing dimensions, dates on stamps.
- If it is still too big: convert color scans to grayscale, drop image resolution to 150 dpi for typed text, and remove embedded attachments. Each of these is a separate, large step down.
- If the quality is unacceptable at the target: stop compressing and split the document instead. A 300-page color scan cannot become a legible 2 MB file. No tool changes that arithmetic.
What to expect at different starting points
These are typical outcomes, not guarantees:
| Starting file | Realistic reduction |
|---|---|
| Color scan, 300 dpi, no OCR | 60–85% (to grayscale, 150–200 dpi) |
| Report with photos exported "high quality" | 70–90% |
| Text PDF from Word / Google Docs | 0–30% — it is already small |
| CAD drawing set, mostly vector lines | 0–20% unless raster backgrounds are the bulk |
| Already-compressed PDF | Often under 10%; sometimes it grows |
If your file is in the last two rows, the lever is not compression. It is removing content or splitting.
FAQ
Can I compress a PDF to exactly 10 MB?
You can land under 10 MB. Compression works in steps (resolution levels, quality levels), so the result lands somewhere below the target — typically within 5–15% of it. Exactly filling a limit has no benefit anyway; portals reject files at the line.
Will the text get blurry?
Not if the text is real text. Vector text is not touched by image compression. Text gets blurry only when the page is a scanned image and the resolution drops too far — below about 150 dpi for normal print, below 200 dpi for small print or handwriting.
The tool says the target is impossible. What now?
Believe it. Then take one of three paths: split the file, convert to grayscale, or accept a lower resolution for pages that are only reference material. For legal and government filings, ask the clerk or help desk — most have a written procedure for oversized documents.