One short certificate
A single page with large type, photographed in daylight and cropped to the paper, is the kind of file that can land under 50 KB. Check the preview at full zoom before you upload. If a line has broken up, do not submit it.
Compress PDF to 50 KB
A PDF that already fits is returned as-is. A bigger PDF is rebuilt as images, so you cannot select the text afterwards.
Page order
About this size
50 KB is a hard ceiling. One clear photo of a single page can fit. A full marksheet, a two-page certificate, or a scan with a colour photo often cannot, not without turning the print into blotches. This page tries 50 KB, stops while ordinary text is still readable, and tells you the real size.
How to use it
- Set the size written on your form. Use Custom if the number is not on a chip.
- Tap Choose PDF or photos. Add one PDF, or all the JPG or PNG photos in page order.
- Wait. You can cancel. The file does not leave this phone.
- Read the size line, look at the preview, then download and upload that PDF on the form.
If the photos are in the wrong order, use Move up and Move down. The PDF is rebuilt on this phone.PDFUnderKB does not see the file.
Limits
- JPG and PNG photos, or one PDF. Up to 8 photos, or 8 PDF pages.
- Up to 8 MB for one file, and 24 MB altogether. Larger files are rejected so the phone does not crash.
- Password-protected PDFs are rejected. Remove the password first.
- Digitally signed PDFs are rejected. Compressing one would break the signature.
- A PDF that is already under the limit is returned as-is, so the text stays selectable. A bigger PDF is rebuilt as images. You will not be able to select the text, and form fields or digital signatures are removed.
- The readable copy keeps the long side of each page at 1,200 pixels or more. We stop there instead of turning small print into blotches. Shrink more is a separate button, and it says the text may be hard to read.
- Sizes here count 1 KB as 1,000 bytes. A file marked under 200 KB is at most 200,000 bytes, so it also fits a portal that counts 1 KB as 1,024 bytes.
- We never add empty data to inflate a file, and we never show a size smaller than the file you download.
Examples
A four-page scan
Four pages at 50 KB is about 12 KB a page. Expect the tool to say the readable copy is over 50 KB. Download that copy only if the form will take it, or split the PDF and ask whether the portal allows more than one upload. Forcing 50 KB would make the text unreadable, so we will not pretend the file is 50 KB.
Common questions
Why will it not just force 50 KB?
Because a file under 50 KB can be a blur, and a blur fails a human check even if the portal accepts the size. If the readable copy is 90 KB, that is the truth. You can tap Shrink more, and the page will warn you to check the words.
Does my file get uploaded?
No. The PDF or the photos are read in this browser and the smaller PDF is built here. There is no account and no upload. Closing the tab drops the in-memory copy. The downloaded file is saved by your phone or computer.
Why can't I select the text in the new PDF?
If your PDF was already under the limit, it is returned unchanged and the text stays selectable. If it was too big, each page is rebuilt as a picture so the file can get small enough. You cannot select text in a picture, and form fields or digital signatures are not copied across. The result tells you which one you got.
What if the form still says the file is too big?
Check the number on the form, then try the next smaller chip. If the page stopped because a smaller file would be hard to read, look at the preview before you tap Shrink more. The size on screen is the real size of the download. Empty bytes are never added to fake a different size.
Will the exam or university accept this file?
This tool only changes file size. A portal can still reject a document because it is the wrong document, the wrong page count, or past a deadline. This site is not the exam body, the university, or a government office. Read the notice on your form before you submit.