Reduce the size of a PDF
A PDF only shrinks a lot if it is made of images. Scans and documents with photographs typically drop between 50% and 90%. A PDF exported from Word or generated by a billing system stores text as vector instructions already compressed with Flate, the same algorithm as ZIP, so it barely shrinks. Compressing a PDF at BestPDFInTheWorld is free, up to 10 MB per file, five times a day, with no account.
Verified 2026-07-31
- Image based PDF (scans, photographs): drops 50% to 90%.
- Vector text PDF (Word, billing systems): barely drops, because it is already Flate compressed.
- Three levels: light renders at 144 DPI with JPEG quality 0.82; medium at 108 DPI with 0.70; strong at 79 DPI with 0.55.
- Compression rasterises: it turns each page into an image, and text stops being selectable and searchable.
- When text must stay searchable, splitting the file or deleting pages solves it with no loss.
Why does my PDF not shrink?
Because it is already compressed. That is the answer in almost every case where someone complains that compression did nothing.
A PDF stores text as vector drawing instructions: which font, which glyph, at which coordinate. That instruction stream is stored with the Flate filter, the same family as the deflate used in ZIP files. It has already been through a compressor. Compressing compressed data gains nothing, and sometimes even grows the file slightly.
If your 30 page document is 400 KB, it is at its practical minimum and there is no work to do. If it is 30 MB, it is almost certainly made of images.
Which kind of PDF you have
| PDF origin | What is inside | How much it drops | What to do |
|---|---|---|---|
| Paper scan | Image (JPEG or CCITT) | A lot, 50% to 90% | Compress |
| Exported from Word | Vector text (Flate) | Almost nothing | Split or delete pages |
| Inserted photographs | Image (JPEG) | A lot | Compress |
| Exported slide deck | Mixed | Moderate | Compress at the light level |
| System generated invoice | Vector text (Flate) | Almost nothing | Already at its minimum |
There is a fast way to find out without opening anything: try to select a word in the document with the mouse. If you can select letters, it is vector text and it will not shrink. If the cursor selects the whole page as one block, it is an image and it will shrink a lot.
The three levels, with the exact numbers
Compression draws each page onto a canvas and re-encodes it as JPEG inside a new PDF. Two parameters decide the result: the scale the page is drawn at, and the JPEG quality. A PDF uses 72 points per inch as its base unit, so scale converts directly into DPI.
| Level | Scale | Resolution | JPEG quality | What it is for |
|---|---|---|---|---|
| Light | 2.0 | 144 DPI | 0.82 | Archiving and reading on a large screen |
| Medium | 1.5 | 108 DPI | 0.70 | Sending by email, everyday use |
| Strong | 1.1 | 79 DPI | 0.55 | Getting under a tight limit |
For reference: 300 DPI is the archival scanning standard, 150 DPI is the comfortable minimum for home printing, and 72 DPI is the historical density of a screen. The strong level sits deliberately near that lower bound, because it exists to solve one concrete problem: getting under a size limit.
What you lose, said plainly
- Text stops being selectable. After compression nobody can copy a sentence out of the document.
- Text stops being searchable. Your PDF reader's search and your operating system's search stop finding words inside the file.
- Links and form fields disappear. What survives is the appearance, not the behaviour.
- Transparency becomes white. The canvas is filled with white before the page is drawn.
- It is irreversible. There is no way back to text from an image without OCR, which we do not do.
Always keep the original. For an invoice, a receipt or a proof of payment that will only be looked at, none of this matters. For a contract the other party will quote, it matters a great deal.
How to get under a specific limit
Ordered by what costs the document least:
- Delete the pages that do not matter. Zero quality loss. Sending 6 pages instead of 80 usually solves it on its own.
- Split into parts. Zero quality loss. Two 15 MB files pass where one 30 MB file does not.
- Compress at the light level. 144 DPI is still readable on screen and printable at acceptable quality.
- Compress at the medium level. The balance for most email sending.
- Compress at the strong level. Last resort, when the limit is tight and the document is for screen reading.
If you need to send by email, the usable limit is about 75% of the advertised one, because the attachment travels base64 encoded and grows by 33%. On Gmail, the advertised 25 MB fits a file of about 18 MB.
Limits of the free tool
Compress PDF is the only one of the twelve tools that works without a subscription: up to 10 MB per file and five uses per day, with no account and no watermark on the result. Above that, or for the other eleven tools, the plan costs EUR 1.99 per month, with no limits and no lock in.
The file is processed in your browser in every case, including on the free tier. The count of the five uses is the only piece of data that leaves your computer, and it is a number, not the document.
Reduce the size of a PDF
How do I get a PDF under 5 MB?
If it is a scan, the medium level usually does it and the strong level almost always does. If it is a text PDF exported from Word, compression will not get you there: delete the pages you do not need or split the file, because the content is already compressed.
Does compressing a PDF lose quality?
Yes, and irreversibly. Each page becomes a JPEG image at the resolution of the chosen level, between 79 and 144 DPI. Text stops being selectable and searchable. Always keep the original.
Which compression level is best?
Medium, at 108 DPI with quality 0.70, for sending by email. Light, at 144 DPI, when the document will be read carefully or printed. Strong only when there is a size limit to meet.
Why did the file get bigger after compressing?
It happens with pure text PDFs of few pages: the original was already optimised with Flate, and turning each page into a JPEG adds data instead of saving it. In that case compression is the wrong tool.
How many times can I compress for free per day?
Five, with files up to 10 MB each, without creating an account. The EUR 1.99 per month plan removes the limit and unlocks the other eleven tools.
Keep reading
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