Free · runs in your browser · the PDF is never uploaded
Compress a PDF to 400 KB
Short answer
Use the compressor below, pre-set to 390 KB so the result passes a 400 KB limit either way. About three to five pages stay sharp; around twelve plain pages usually fit at the lowest setting.
What fits in 400 KB
- Comfortably: Three to five pages at good quality, or a short text report unchanged.
- At the limit: Around twelve plain pages at the lowest setting.
400 KB appears on some exam and job portals that sit between 300 KB and 500 KB caps.
Merged mark sheets or a short multi-page scan often land here after a single Target size pass.
“Good quality” here means around 100 DPI, which looks sharp on a screen. These are rough guides, not promises: a page of plain text compresses far better than a colour photo, so check the preview.
How to compress a PDF to 400 KB
- 1
Drop your PDF into the compressor above, or tap it to choose a file. It’s already in Target size mode at 390 KB.
- 2
Press Compress. A lossless rebuild runs first. If the file is still too big, the pages are re-rendered at lower resolutions, from 150 DPI down to 50 DPI, until it fits.
- 3
Check the preview of the first pages. Zoom in on the small print, such as dates, ID numbers and stamps, because that’s what blurs first.
- 4
Download the file and check its size on your device before uploading. On Windows, right-click and choose Properties; on a Mac, use Get Info. Compare the size in bytes with the limit.
- 5
Upload it. If the portal still says the file is too big, run the compressor again on the original with a slightly lower target.
Why the tool is set to 390 KB, not 400 KB
Kilobytes are counted two ways. Some websites treat 1 KB as 1,000 bytes; others, and this compressor, treat it as 1,024. A file the compressor calls “400 KB” is 409,600 bytes, about 2.4% more than 400,000, and a strict portal will reject it.
390 KB in the tool is 399,360 bytes, which is under 400 KB by either definition. You lose almost nothing in quality and avoid the most common “file too large” rejection.
If it won’t get down to 400 KB
The compressor stops at 50 DPI, because below that the text stops being readable. If even that pass is too big, you get the smallest readable file and a message saying so, instead of a file that technically fits but that nobody can read. These help:
- Delete pages the form does not ask for before compressing.
- Prefer digital PDFs over photographing printouts when you have them.
- Check the preview on seals and handwritten marks.
- Split the document if the portal has more than one upload field. Split PDF breaks it into parts you can compress separately.
Limits worth knowing
- Re-rendered pages become images with an invisible text layer. Search and copy keep working, but accented and non-Latin characters can be dropped from that layer.
- Large or image-heavy PDFs take a while, because each pass re-renders every page on your device.
- Password-protected PDFs have to be unlocked first.
- A portal can reject a file for reasons other than size, such as the file type or characters in the file name.
Frequently asked questions
How do I compress a PDF to 400 KB?
Open this page, drop the file, and press Compress. The tool is already set to 390 KB.Why is the target 390 KB?
To stay under 400,000 bytes whether the portal counts 1 KB as 1,000 or 1,024 bytes.Does compression upload my file?
No. It runs in your browser.
Guides for upload limits
- PDFs for government formsFrom phone photo to a PDF that passes the portal’s size limit, plus what you can and can’t hide.
- Exam application documentsMake a reusable “upload kit” of your certificates at the sizes exam forms ask for.
- Job and onboarding documentsPayslips, certificates, relieving letters and ID for HR portals, sized and checked.
- Visa application documentsUnlock bank statements, merge by category and get each file under the upload limit.
- PDF upload size limitsTypical caps for email and portals — and how to shrink toward them privately.
Written by Sumit · Last reviewed 12 Oct 2026