How to Compress a PDF Online (and What It Does to Quality)
"Without losing quality" depends on what is in the PDF and how the compressor works. Here is what this tool actually does to your pages, which settings matter and which files you should not compress at all.
Drop a PDF, pick Quality % or Target file size, press Compress PDF and check the size in the result line.
First, what "compress" means in this tool
Most PDF compressors quietly recompress the images inside a file and leave everything else alone. Compress PDF works differently, and knowing how decides whether it is the right tool for your file. It draws every page, saves that picture as a JPEG, and builds a new PDF in which each page is just that JPEG, at the original page size.
That has two big consequences. Scanned documents and image-heavy files shrink a lot, because they were pictures to begin with. Text-based documents lose something: the text turns into pixels, so it can no longer be selected, searched or copied, and links and form fields stop working. For a small text-only PDF the new file can even be bigger than the original, because a page of pixels is heavier than a page of letters.
Compress a PDF in five steps
- Open the tool and drop your PDF on Drop a PDF here, or click the box and choose the file.
- Pick a Compression mode: Quality % or Target file size.
- Set the controls for that mode (explained below) and the Render DPI slider.
- Press Compress PDF. The status shows "Compressing..." and a progress bar fills as each page is processed.
- Read the result line, for example "Reduced from 18 MB to 4 MB (78% smaller)", then press Download PDF. The file keeps its name with
-compressedadded before .pdf.
The three controls and what they trade
| Control | Range | Raising it gives you |
|---|---|---|
| Image quality (Quality % mode) | 10 to 100, starts at 60 | Cleaner pages, bigger file |
| Render DPI | 72 up to about 150, starts at 96 | Sharper small text, much bigger file |
| Target size (Target file size mode) | a number plus KB or MB | The tool picks the quality for you |
DPI has the larger effect on size, because doubling the resolution quadruples the number of pixels per page. A good habit is to leave quality at the default, try one run, and read the result before touching anything else.
How the target size mode really behaves
In target mode the tool estimates a quality from the target and your original file size, then makes one pass. It is a rough estimate, not a search that keeps trying until it lands on the number. Expect the output to be near your target, sometimes over it, and the quality is kept between 10 and 95 percent. If the result is too big, run it again with a lower target, or lower the DPI.
Which files compress well and which do not
- Scans and photo PDFs. Excellent results. A 40 MB scan can become a few megabytes.
- Slide decks exported with large pictures. Good results, but fine text on slides may soften at low DPI.
- Text documents, contracts and forms. Usually a poor fit. They are already small, and rasterising removes text selection and form fields.
- Files that must remain searchable. Do not use this tool. Reduce the size by other means, such as removing pages.
An illustrative example
Take a 30-page phone scan that weighs 45 MB and has to fit a 10 MB upload field. Start with the defaults, which are quality 60 and DPI 96, and read the result line. If it says something like "Reduced from 45 MB to 9 MB", you are done, provided the small print is legible. If it still lands at 12 MB, lower the quality in steps of 10 on the original file rather than recompressing the output. These numbers are only an illustration, since every scan behaves differently, which is exactly why the result line is worth reading each time.
Checking the result before you send it
Open the compressed file and look at the page with the smallest text. If you can read it at normal zoom, the settings are fine. If it looks soft, go back to the original, raise the DPI one step and compress again. Compress the original each time, never an already compressed copy, because repeating the process stacks the JPEG damage.
Better ways to get a smaller PDF
Often the biggest saving comes from removing pages, not squeezing them. Drop blank sheets with Delete PDF Pages, or send only what is needed using Extract PDF Pages. When the size limit is strict, how to make a PDF under 1 MB, 2 MB or 5 MB walks through the options, and what actually works when a PDF is too large to email covers sending large files. For a PDF built from photos, shrinking the photos first with Compress JPG is often better than compressing the finished PDF.
Frequently Asked Questions
Does Compress PDF keep my text selectable?
No. Each page is redrawn as a picture, so text, links and form fields become part of the image and can no longer be selected or searched.
Why did my PDF get bigger after compressing?
Small text-only PDFs are already compact. A page stored as a picture can weigh more than the same page stored as text. Keep the original in that case.
What is a good Render DPI for scans?
The default of 96 suits many scans read on screen. Raise it one step at a time if small print looks soft. Higher values make the file much larger.
Will target size mode hit my number exactly?
Not always. The tool estimates a quality from the target in one pass, so the result can land above or below it. Lower the target and try again if it is too big.
Can I compress a PDF several times to make it smaller?
Compress the original each time instead. Compressing a compressed file repeats the JPEG loss and usually gives poorer results for little extra saving.
What is the downloaded file called?
Your original file name with -compressed added before .pdf, so the original is never overwritten.