PDFUnderKB

Compress a PDF or photos

Size limit

A PDF that already fits is returned as-is. A bigger PDF is rebuilt as images, so you cannot select the text afterwards.

About this size

The form wants a PDF under a size in KB. Pick that number, add the PDF or the photos of the pages, and download a smaller file. The work happens on this phone. 200 KB is selected because that is the limit people hit most often. Change the chip if your form says something else.

How to use it

  1. Set the size written on your form. Use Custom if the number is not on a chip.
  2. Tap Choose PDF or photos. Add one PDF, or all the JPG or PNG photos in page order.
  3. Wait. You can cancel. The file does not leave this phone.
  4. 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

One PDF the portal rejected

The upload box says the maximum is 200 KB and your scan is 2 MB. Select 200 KB, add that one PDF, and wait. If it was already small enough, you get the same file back and the text stays selectable. If it was too big, you get a picture PDF and a preview so you can check the words.

Front and back, photographed

You have two JPG photos and the form wants one PDF. Select both, put them in order with Move up and Move down, and download one PDF. Do this only if the form allows that document.

Common questions

Which size should I pick?

Use the number printed on your form. The chips are 50, 100, 200, 300, and 500 KB. Custom accepts any whole number from 20 to 2048 KB. Do not guess a smaller number than the form allows if the preview is already sharp and under the limit.

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.

Other limits