How to Compress a PDF to 100KB for an Upload Portal — and What to Do When It Won't Fit
Get a PDF under 100KB, 200KB, 500KB or 1MB for a government, exam or job portal: what makes PDFs big, the right order of steps, and what to do when a scan won't fit.
Updated September 15, 20267 min read
To compress a PDF to 100KB, first remove every page the portal does not need, then compress what is left with settings that shrink the pictures inside the file and leave the text alone. Whether 100KB is reachable at all depends on one question: is your PDF made of text or of scanned pages? A letter exported from Word is often under 100KB already, while a single colour scan from a phone can be well over a megabyte. This guide explains why, gives the order of steps that gets a document under a hard KB cap, and covers what to do when a scan simply will not fit.
What makes a PDF too big for the portal
Government, exam and job portals set hard caps — 100KB, 200KB, 500KB, 1MB — and the page count has much less to do with the size than what is inside each page.
| What is inside | What it costs | What shrinks it |
|---|---|---|
| Text from Word or a filled-in form | Very little — several pages often fit in 100KB | Not much; it is already small |
| Scanned pages | A full photograph per page | Lower resolution, stronger compression, grayscale |
| Photos pasted into a document | As much as the original photos | Recompressing them at the size they are shown |
| Embedded fonts | A share of the budget in a very small file | Usually nothing — they draw the text |
The quick test: try to select a line of text. If words highlight, the text is real text. If your cursor draws a rectangle, every page is a picture. An A4 page scanned at 300 DPI is about 2480 × 3508 pixels — nearly nine million — and even a well-compressed picture that size runs to several hundred kilobytes on its own. That is why one scan can blow a 100KB budget that ten typed pages would fit into. For the wider picture on the two kinds of PDF, see compressing a PDF without wrecking the text.
The order of operations
Read the notice
Check the exact limit, whether it wants one file or one per document, and whether photos and signatures go up as JPG rather than PDF. Limits differ between portals and between application rounds.
Remove pages before compressing
Blank backs of single-sided documents, instruction sheets, duplicate scans. Every scanned page you remove gives back its whole share of the budget. The page remover can find blank pages and duplicates for you, or take a range you type.
Merge first, compress once
If the portal wants several documents in one file, join them with the PDF merger in the order the notice lists, then compress the combined file a single time.
Compress in Strong
The 100KB page opens our compressor in Strong: pictures recompressed at 96 DPI, while text, links and form fields stay exactly as they were. Before you run it, the estimate under the mode picker shows the predicted size for your file.
Read the size line, then the pages
The result says in plain words whether the file is under 100KB or still over. Then open it at 100% zoom — being under the limit does not help if the reviewer cannot read it.
What is free and what is Pro
All four modes — Lossless, Balanced, Strong and Flatten — are free, and so is the line that tells you whether the result fits. The free plan handles one PDF at a time, up to 25MB and 100 pages. Pro adds manual control of quality, resolution, grayscale and metadata removal, and an automatic target: type 100KB, 500KB or 1MB and the tool searches for the gentlest settings that fit, instead of you trying modes by hand. If you ask for less than the file can possibly reach, the field says so and names the smallest size it can manage.
Hitting 200KB, 500KB or 1MB
A bigger cap is not just the same job with more room; it lets you keep more detail. Aim for the gentlest mode that still fits.
| Limit | What usually fits | Start with |
|---|---|---|
| 100KB | A text PDF of several pages, or one or two scanned pages | Strong, after removing every page not asked for |
| 200KB | Two to four scanned pages at 96 DPI | Strong on the 200KB page |
| 500KB | Roughly five to ten scanned pages at 96 DPI | Strong, or Balanced if the pages are simple |
| 1MB | Several scanned pages at the sharper 150 DPI | Balanced — pictures stay at 150 DPI |
Balanced keeps pictures at 150 DPI, the usual standard for on-screen reading and office printing, so when the limit allows it the reviewer gets a noticeably crisper page. Treat the table as a starting point: a busy colour page costs far more than a plain typed one, and the estimate for your own file is the number that counts.
Opens in Strong and tells you whether the result is under 100KB. It all runs on your device, not our servers — which matters for ID cards and certificates.
Compress a PDF to 100KBWhen a scan will not fit in 100KB
Some documents cannot reach 100KB and stay readable: a ten-page colour scan, a certificate scanned at high resolution on a patterned background. The options, in order of how much they buy you:
- Fewer pages. Send only what the notice lists. This is the single biggest lever for a scan.
- Rescan in grayscale at 150 DPI. A black-and-white document scanned in colour spends bytes on colour nobody needs, and compressing a smaller, cleaner scan beats squeezing a large one. On Pro, the compressor's grayscale option does the same to a scan you already have.
- Split into separate uploads. If the portal takes one file per document, the PDF splitter extracts each document into its own file, or packs pages into as many files as it takes to stay under a size you set. Splitting a PDF covers the page-number pitfalls.
- Upload an image instead. If the portal accepts JPG for that document, a one-page scan as a JPG is often just as readable — resizing an image in KB for online forms covers that route.
One option that rarely helps a scan is Flatten. It turns each page into a single picture at 96 DPI, which is useful when a page is full of vector drawings, but on a page that was already a photograph it usually comes out larger than Strong. Check its estimate before you pick it.
Before you upload
Keep the original, uncompressed file. If the portal later asks for a clearer copy, or a different round sets a different limit, you want to compress again from the source rather than squeeze an already compressed file a second time, which costs quality at every pass. And check the page order one last time: reviewers look for documents in the sequence the notice lists them, not the order your scanner produced.
Frequently asked questions
How do I compress a PDF to 100KB?
Remove any pages the portal does not need, then open the PDF in the 100KB compressor, keep the Strong mode it starts in and press Compress. The result tells you whether it is under 100KB. If it is not, split the document, rescan in grayscale at 150 DPI, or upload the page as a JPG if the portal accepts one.
Why is my PDF still over 100KB after compressing?
Almost always because it is a scan with several pages, or a colour scan at high resolution. Each scanned page is a photograph, so the budget per page is tiny. Fewer pages and a grayscale rescan move the number far more than any compression setting.
How do I reduce a PDF to 200KB, 500KB or 1MB?
The same way, with more room to keep detail. Use the 200KB page for that cap; for 500KB or 1MB, try Balanced first in the PDF compressor, which keeps pictures at 150 DPI, and drop to Strong only if the estimate is over. On Pro you can type any target and let the tool find the settings.
Can I compress a PDF to 100KB for free?
Yes. Every mode is free, and the result tells you whether it is under 100KB, for one PDF at a time up to 25MB and 100 pages. The automatic target search, where you type a size and the tool finds the settings, is part of Pro.
Will compressing make my PDF blurry?
Not the text in a typed PDF: Strong recompresses only the pictures and leaves text, links and form fields as they were. In a scan the text is part of the picture, so small print can soften at 96 DPI — open the result at 100% zoom and check before you upload.