The short answer
Text is cheap: a full page of typed text usually takes 5 to 50 KB. Images are expensive: one color page scanned at 300 DPI or one photo straight from a phone can take 1 to 5 MB. So if your PDF is many megabytes, look for scans and photos first.
To fix it, drop the file into the compressor below and keep the Medium level. It finds the images inside the PDF, scales down the ones that are larger than needed and saves them again as JPEG, while text, vector graphics, links and form fields are left alone. You see the size before and after, and if the result would not be smaller, you get your original file back.
Try it here: Compress PDF
Open the full tool pageWhat actually takes up the space
A PDF stores each kind of content in its own way, and the differences in size are huge. These are the usual suspects, roughly from biggest to smallest.
- Scanned pages: a scan is a photo of the paper. An A4 page at 300 DPI is about 2480 by 3508 pixels, which is around 26 MB of raw color data before compression. Even compressed, color scans are often 0.5 to 3 MB per page.
- Photos inserted at full size: a 12 megapixel phone photo placed in a Word document keeps all its pixels in the PDF, even if it is shown as a small picture. A brochure with ten of them can easily reach 20 to 40 MB.
- Images saved without lossy compression: screenshots and graphics are often stored losslessly, which is fine for sharp diagrams but heavy for photos.
- Embedded fonts: a PDF carries the fonts it uses so it looks the same everywhere. Usually only the used characters are stored (a subset of 20 to 100 KB), but some programs embed complete fonts, and a full Chinese, Japanese or Korean font can be several megabytes on its own.
- Incremental saves: some PDF editors and signing tools append changes to the end of the file instead of rewriting it. Every edit, comment or signature adds a new layer, and old versions of changed objects stay inside the file.
- Extras: attachments, embedded audio or video, and duplicate copies of the same image on many pages when the file was assembled carelessly.
Typical sizes per page
Use this table to judge whether your file is reasonable. Divide the file size by the page count and compare. Exact numbers depend on the content, so treat them as ranges.
| Kind of page | Typical size per page | After compression |
|---|---|---|
| Typed text from Word or Google Docs | 5 to 50 KB | Little or no change, nothing to gain |
| Black and white scan, 300 DPI | 30 to 150 KB | Usually already small |
| Grayscale scan, 200 DPI | 100 to 400 KB | About 60 to 200 KB |
| Color scan, 300 DPI | 0.5 to 3 MB | About 150 to 500 KB |
| Phone photo of a document | 2 to 5 MB | About 200 to 600 KB |
| Slide or brochure page with photos | 0.3 to 3 MB | Often half or less |
How to make it smaller without ruining the text
The goal is to shrink images and leave text alone. Text and vector graphics are stored as shapes, not pixels, so they stay sharp at any zoom level and take almost no space. Turning them into images is what makes cheap compressors produce blurry, unsearchable files.
The compressor on this page offers three levels that only touch images. Light keeps images up to about 300 DPI, Medium up to about 200 DPI, which is plenty for screen and office printing, and Strong up to about 150 DPI for the smallest file with text intact. Masks, CMYK images and other special image types are left as they are so colors do not shift.
For documents that are scans from start to finish, there is a fourth level, Pages to images. Every page is rendered and saved as one compact JPEG. This can shrink large scans dramatically, but text that was selectable before (for example in a scan that went through OCR) can no longer be selected. Use it only for scans.
If you have a hard limit, such as 2 MB for an email or 500 KB for an application form, choose Target size and type the limit in KB. The tool lowers image quality step by step and keeps the first version that fits. Pages are turned into images only if that is not enough, and the result row tells you when that happened.
Avoid large PDFs at the source
The best compression is the one you do not need. A few settings when creating the PDF make a big difference.
- Scan documents in grayscale at 200 DPI unless you need color. Black and white mode at 300 DPI is even smaller for plain text pages.
- Shrink photos before inserting them into Word or PowerPoint. In Word for Windows, File > Save As > PDF has an option called Minimum size (publishing online) that lowers image resolution in the PDF.
- When a PDF has been edited, signed or annotated many times, save it under a new name with Save As. Many editors rewrite the file completely then, dropping old versions.
- Delete pages you do not need before sending: blank scanner pages, duplicate covers or appendices nobody asked for.
- Merge first, compress once. Compressing each part and merging later often gives a bigger file than compressing the merged one.
Built in options and their catch
On a Mac, Preview can shrink a PDF with File > Export and the Quartz Filter called Reduce File Size. It works without installing anything, but it is aggressive: images often become blurry and the setting cannot be adjusted. Adobe Acrobat has a Reduce File Size command, but only in the paid version.
Online compressors that upload your file can produce good results, but the document leaves your device. For contracts, bank statements, medical letters and IDs that is a real concern. The tool on this page does all the work in your browser, so the file never leaves your computer or phone.
When the file barely gets smaller
If the compressor reports that the file is already well compressed, the PDF contains mostly text or its images are already small. There is nothing large left to shrink, and pushing further would only damage quality.
If a scanned PDF does not shrink enough with Strong, try Pages to images. If it is still over your limit, remove pages you do not need with Organize PDF, or split the document into parts if the recipient accepts several files. Password protected PDFs cannot be compressed until the password is removed in your PDF reader.