How to compress a PDF to under 100 KB (and what to do when it won't go)

An upload form has just told you your file is too large. It wants 100 KB. You have 3.4 MB, and a deadline.

Almost every guide to this problem gives you the same advice — compress the PDF online with a free tool and you're done — which works perfectly for about half of the people who read it and fails completely for the other half. Which half you're in was decided before you started, by what is actually inside your PDF.

So this guide starts there, because five seconds of diagnosis saves you twenty minutes of compressing a file that was never going to get smaller.

How to compress a PDF to 100 KB online, free

Compress PDFShrink PDF file size losslessly — no quality lost, nothing uploaded.

If your PDF came out of Word, Excel, Google Docs, LaTeX, or any "Save as PDF" button, drop it in and it will shrink losslessly. If your PDF is a scan or a photo — anything that started life in a scanner or a phone camera — compression alone will not get you to 100 KB, and the section below on scanned documents is the one you want.

First: which kind of PDF do you have?

Open the file and try to select a sentence with your mouse.

• The text highlights. You have a text-based PDF. Its size is structure, fonts, and vector graphics. This compresses well.
• Nothing highlights, or you select a whole rectangle at once. You have a scanned or image-based PDF. Every page is a photograph of a document. Its size is image data, and that data is already compressed.

That single test decides everything that follows. A 3 MB text PDF and a 3 MB scan are the same number describing two completely different problems.

How to compress a text-based PDF (the easy case)

This is the easy case, and it is the one our free online PDF compressor is built for.

1. Open the PDF. Drag it onto the drop zone or click to browse.
2. Click Compress PDF. The document is rebuilt — objects nothing references any more are dropped, and the cross-reference tables are packed tight.
3. Read the before and after. The new size sits next to the original, so you know what you saved before you download anything.

The saving here is completely lossless. Nothing is re-rendered, re-sampled, or re-encoded. Every glyph, image, and vector comes through bit-for-bit identical — the file gets smaller, the pixels are untouched.

Files exported from word processors carry a surprising amount of dead weight: revision leftovers, embedded font subsets for characters the document never uses, duplicated resources on every page. Reports, invoices, and Word exports often shed a satisfying chunk.

If it's still too big

A text PDF that stays stubbornly large usually has one of three things in it:

• A logo or header image on every page, especially a PNG screenshot. Replacing it with a smaller image before exporting is worth more than any compressor.
• Fully embedded fonts rather than subsets. Re-exporting with "subset fonts" enabled in your source application fixes this at the source.
• Pages you don't need. Cutting the file down is compression too, and often the biggest single win. Use Delete Pages or Extract Pages to keep only what the form actually asked for.

How to compress a scanned PDF (and why the size won't budge)

Here is the part most articles skip.

A scanned page is a JPEG. JPEG is already a compressed format, and it was compressed by your scanner at whatever quality it was set to. Running a PDF compressor over it asks the tool to squeeze something that has already been squeezed. There is nothing structural left to remove — the file is 95% image data and 5% PDF wrapper, and only the wrapper is on the table.

Our compressor will report a saving of a percent or two on a scan and we would rather tell you that up front than hand you a "compressed" file that is the same size and let you discover it at the upload form.

The route that actually works

To genuinely shrink a scan, you must reduce its resolution — the pixel count — rather than hunting for redundancy that isn't there. That means taking the pages out as images, shrinking those, and rebuilding the PDF:

1. Convert the PDF to JPG at 72 or 150 DPI. Not 300. A 300 DPI scan of an A4 page is roughly 2480 × 3508 pixels, which is far more detail than any form reviewer needs and is the single biggest reason your file is large.
2. Compress the images with the quality slider. Watch the preview — for a document of printed text you can usually go a long way down before it looks wrong.
3. Turn the images back into a PDF, in order, as one file.

A scan that refused to move below 3 MB routinely lands between 80 KB and 300 KB through this route, and the text stays readable because you chose the trade-off deliberately instead of a tool making it for you.

How much can you reduce a PDF file size?

How far you can reduce the PDF file size depends entirely on the diagnosis above. Rough expectations, so you know whether to keep compressing or change approach:

"Via the image route" means the three-step process in the section above, not a compressor.

PDF size limits on Indian government portals

This is where the 100 KB number comes from for a great many people. Recruitment and examination portals enforce some of the tightest upload caps anywhere, and they reject rather than warn.

The common ones, as a rough guide — always check the notification for your specific form, because these change between cycles and between states:

Three things worth knowing before you fight one of these forms:

The cap is usually on the scan, not on your typing. Certificates, mark sheets, and caste or income documents are scans, so they are the hard case — use the image route above rather than expecting a compressor to manage it.

Check whether the failing upload is even a PDF. A large share of "file too large" errors on these portals are the photograph and signature fields, which want a JPG of 20–50 KB at a specific pixel size. That is an image job, not a PDF job: Resize Image for the dimensions, then Compress Image for the weight.

Scan in grayscale at 150 DPI from the start. Colour roughly triples the size of a document scan and almost no portal requires it. This one setting solves the problem more often than any tool does.

Compress a PDF online without uploading it anywhere

Every step described here runs inside your browser tab. Your PDF is not uploaded, not queued, and not stored — there is no server copy to delete afterwards, because one was never made.

That matters more than usual for this particular job. The documents people compress to meet an upload cap are ID cards, certificates, bank statements, and mark sheets: precisely the files you would least like sitting in a stranger's temporary directory.

You do not have to take our word for it. Open your browser's developer tools, switch to the Network tab, and compress a file. You will see the page's own assets load, and nothing carrying your document.

Four tools on this site genuinely do need a server — converting to and from Word, PowerPoint, and Excel — because rebuilding an editable document out of positioned glyphs is analysis no browser library performs. Each one says so on its page, above the file picker. Compression is not among them.

Compress PDF: common questions

Will compressing a PDF reduce its quality? Not with the lossless rebuild described here — nothing is re-encoded. It absolutely will if you take the image route, which is why that route is a deliberate choice with a preview at each step rather than the default.

Why did my PDF get bigger? Occasionally a file is already optimally packed and the rebuild adds a few bytes of structure. If that happens, keep your original — the tool shows you both sizes precisely so you can make that call.

Can I compress a password-protected PDF? Remove the password first with Unlock PDF — a tool cannot rewrite a file it cannot read. You can protect it again afterwards with Protect PDF.

Is there a file size limit? No account limit and no page limit — the practical ceiling is what your device can hold in memory, which is far more generous than the queue-and-wait limits of upload-based services.

What if I only need part of the document? Then that is your compression. Split PDF or Extract Pages will get a 40-page file under a cap that the full document was never going to meet.

Where to start compressing your PDF

If you have a text-based PDF, start and probably finish with the compressor. If you have a scan, skip it and go straight to the three-step image route — you will get there faster by not trying the thing that cannot work.

Compress PDFShrink PDF file size losslessly — no quality lost, nothing uploaded.

Either way, the rest of the free online PDF tools run the same way: in your browser, with no account, no watermark, and nothing uploaded.