Compress PDF to 400 KB
400 KB is the first size on the ladder where you get a real choice: keep a couple of pages in color, or keep several pages sharp in grayscale. The target is preset; this page helps you decide how to spend it.
Compress PDF
or drop PDF files here ·
Max 95 MB per file· Up to 20 files· Deleted after 30 minutes
Files are processed on our servers and deleted after 30 minutes.
Images above this DPI are downsampled. 150 is sharp on screen and fine for office printing; 72 is screen-only.
JPEG quality for re-compressed images. 70 keeps scanned text readable; below 40 artefacts appear around letters.
When aiming for a target size, image quality never drops below this; resolution is reduced instead.
How to use this tool
- 1
Upload your PDF
Drop one PDF or a batch of up to 20, each as large as 95 MB. Phone scans, office scanner output and exported documents all work.
- 2
Decide color or gray
The Target size is 400 KB. Leave Convert to grayscale off for color stamps or photos; turn it on for text-heavy pages.
- 3
Compress and compare
Press Compress and open the result next to the original. If small print looks soft, run it again with grayscale on.
At 400 KB the question changes from "will it fit" to "what should look best": the colored seal on page one, or the small print on pages two to five.
Where 400 KB PDF limits are used
Upload limits around 400 KB are common for documents that carry official marks: educational certificates with a university seal, experience letters on colored letterhead, and no-objection certificates with a stamp and a signature. State recruitment portals in India and some university admission systems use limits in this range so that a reviewer can still verify those marks on screen, while keeping a large applicant pool's storage in check.
The source file is usually the problem. A flatbed scanner set to 300 DPI saves an A4 page as about 8.7 million pixels, roughly 26 MB of raw color data before compression, and a phone scanner app is not much smaller. The compressor has to cut a multi-page scan by a factor of fifty or more, and how it does so decides what the reviewer sees.
Which resolution a 400 KB PDF ends up at
- 72 DPI
Screen only; ten or more scanned pages
- 100 DPI
Six to eight grayscale pages; small print gets soft
- 150 DPI
Three to five grayscale pages, or two in color
- 200 DPI
One or two pages; seals and fine lettering stay clear
- 300 DPI
Rarely reachable at 400 KB except for one light page
Color or grayscale for a PDF under 400 KB
Keep color
- Colored seals, holograms and photos stay recognizable
- Reviewers can tell an original stamp from a photocopy
- Best for one or two pages
Switch to grayscale
- Roughly half the bytes per page, so more pages fit
- Small print stays sharper at the same 400 KB
- Best for transcripts, letters and long statements
Behind both choices the method is the same. UltKit re-encodes each page image as JPEG, starting high and lowering quality until the file fits; once quality would fall below Lowest image quality it reduces resolution instead. Ghostscript, the engine behind many free compressors, names its presets after the same steps: /screen at 72 DPI, /ebook at 150 DPI and /printer at 300 DPI. A 400 KB target usually lands between the last two for short documents.
Text and vector graphics are kept as they are, so a PDF exported from Word or Google Docs barely changes. If you are scanning specifically for an upload, set the scanner to 200 DPI; the guide to scanning documents to PDF has app-by-app settings.
400 KB PDF questions
Is 400 KB enough to keep a colored seal on a certificate?
For one or two pages, yes. Seals, signatures in blue ink and colored letterheads stay recognizable at 400 KB around 150–200 DPI. Past three color pages the tool starts lowering resolution and the seal's fine lettering softens first.
How do I compress a PDF to under 400 KB on a Mac without Preview's filter?
Preview's Export dialog offers a Quartz filter called Reduce File Size, but it has no target and often blurs scans far more than needed. Upload the PDF here in Safari or Chrome instead; it works the same on macOS, Windows and phones, with no app to install.
Why did the tool keep my 380 KB PDF almost unchanged?
It was already under the target, so there was little to remove beyond metadata and unused font data. The result can be a few kilobytes smaller, never forced larger. For a bigger saving on a file that already fits, use Recommended mode instead of Target size.
Can I turn photos of documents into a 400 KB PDF directly?
Yes: image to PDF under 400 KB builds the PDF from your photos and sizes it in one step, which saves converting and then compressing.
Will a 400 KB PDF print clearly?
One or two pages print well, since the file keeps about 200 DPI. A long document squeezed into 400 KB prints at newspaper-like sharpness: readable, but not suited to archiving.
Do two 400 KB fields allow me to upload one 800 KB file?
No. Portals check each upload against its own limit, so a combined file is rejected even if the total is the same. Keep documents separate when the form has separate fields.
