How to Compress a PDF to 100 KB or 200 KB on Your Phone
Updated: 2026-10-18
Online forms often say "PDF only, maximum 100 KB" or "up to 200 KB", while a scanned certificate from a phone camera can easily be 2 or 3 MB. This guide shows how to bring a PDF under the limit on a phone without installing an app, and how to handle files that are too large even after compressing.
Why scanned PDFs are so large
A PDF made from phone photos stores each page as a full-size camera picture, often 12 megapixels or more. That detail is far more than an online form needs. Compressing redraws each page at a sensible resolution and quality, which removes most of the weight while keeping the text readable.
Step by step
Open the Compress PDF tool on PDFPixo in your phone browser. Choose the PDF from your Files or Downloads. In Target size, type the limit from the form, for example 100. Press Create file and wait a few seconds.
The new size is shown before you download. Open the result once and zoom in on the smallest writing, such as roll numbers and dates, to make sure it is still clear. Then upload it to the form.
There are also ready pages with the limit already filled in, for example "Compress PDF to 100 KB" and "Compress PDF to 200 KB".
If the target cannot be reached
PDFPixo will not hand you an unreadable file just to meet a number. If 100 KB would make the pages blurry, it stops and tells you the smallest size it managed. Then try one of these:
Remove pages the form does not need with the organise tool. Split a long PDF and upload only the required pages. Make the PDF again from new scans in black and white with the scan tool, which produces much smaller pages. Check whether the form accepts a slightly larger file for that document.
What changes in the compressed file
Pages are stored as pictures, so the text in the compressed copy cannot be selected or searched, and links stop working. This is fine for forms, which only need to show the document. Keep your original PDF in case you need to edit or print it later.
Tips for very small limits
A single-page document reaches 50 or 100 KB much more easily than a five-page one. Black and white scans are much smaller than colour photos. A clean, straight scan without shadows compresses better than a dark, tilted photo, because shadows and noise add weight.
A worked example
A student has a two-page marksheet PDF of 2.4 MB made from phone photos, and the admission form allows 200 KB. She opens Compress PDF, types 200 and presses the button. The result is about 150 KB and the marks are clear when zoomed in. For another form that allows only 100 KB, the same file reaches 96 KB at a slightly lower resolution; the small print is still readable, so she uploads it.
Quality, resolution and target size together
Without a target, the quality slider and the resolution choice decide the result: Standard resolution gives the smallest files and is fine for forms, while High keeps small print sharper. With a target, PDFPixo tries several combinations and keeps the clearest one under your limit. Setting the target slightly below the limit, for example 95 for a 100 KB limit, leaves a little room in case the portal counts size differently.
Before you start: a short checklist
Find the exact limit in the form, including whether it says KB or MB; 1 MB is 1024 KB. Check whether the form wants one file for all documents or one file per document, because a single combined file needs a larger limit. Make sure the PDF opens without a password; locked files must be unlocked first. If the document is a phone photo rather than a PDF, convert it with the scan tool first, choosing black and white for text documents, because a clean scan compresses far better than a raw photo. Finally, keep the original file safe in a folder you can find again; if the form is rejected later for a blurry document, you can make a clearer copy within a slightly larger limit.
Private by design
The PDF is compressed inside your browser. Certificates, marksheets and ID proofs never leave your phone.
Frequently asked questions
- How do I compress a PDF to 100 KB on mobile?
- Open Compress PDF in your phone browser, choose the file, type 100 in Target size and press Create file.
- Why can I not select text after compressing?
- Pages are saved as pictures to make them small. Keep the original if you need the text.
- My PDF is already small. Why did nothing change?
- If it is already under your limit or well compressed, PDFPixo keeps it as it is instead of making it worse.
- Can I compress many pages to 100 KB?
- Sometimes not without making them unreadable. Remove extra pages or split the file.
- Is there a daily limit?
- No. The tool is free with no sign-up and no daily limit.