Choose how hard to compress
The Compression level field takes a number from 1 to 9. Level 1 keeps the most quality and level 9 makes the smallest file. The field opens at 4, and an empty field is treated as 4 as well.
Compress PDF
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Files other than PDF are converted first. Signing in raises the size limit.
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- One PDF
- You set
- A compression level from 1 to 9
- You get
- The PDF saved at that level
To compress a PDF, add the file, choose a compression level from 1 to 9 and download the result. Levels 1 to 3 only repack the file's structure. Levels 4 to 9 also shrink the images, which are often the heaviest part of a PDF. Start at 4: level 1 keeps the most quality and level 9 makes the smallest file. The result is a new PDF and the copy on your device stays as it was. How much smaller it gets depends on what is inside, so compare the two sizes and check the pages before you send it.
What can you do when you compress a PDF?
See the size before you run
Once you add a file, the file card shows its name and its size in MB. Write that number down so you can compare it with the download. Press Replace if you picked the wrong file.
Stay inside the range
A level below 1 or above 9 does not start the job. The form shows the minimum or the maximum under the field, and you correct the number before you run it.
Get a plain PDF back
The output format is PDF, the same as the input. The job runs the compression step and nothing else, and indox adds no watermark to the result.
What compression keeps and what it changes
Stays the same
- Every page, in the same order. Compression does not remove pages.
- Text stays text. The tool shrinks images and file structure, and it does not remove the words.
- The output is a PDF that opens in any normal viewer.
- The file on your device. You download a new copy.
Changes
- Levels 1 to 3: the file is repacked with compressed streams and object streams. The pages look the same, and the saving can be small.
- Levels 4 to 9: images are resized and saved again as JPEG at lower quality, so photos and scans lose detail as the number rises.
- Levels 6 to 9 can also rewrite the whole file with lower image resolution and subset fonts, so check fine print and charts.
- Levels 4 to 9 may drop objects that nothing in the file points to.
- The PDF version can be raised to 1.5, which a very old viewer may not read.
Which compression level for which job
| You want to | Start at level | Check after |
|---|---|---|
| Email a text-heavy report | 4 | Read the small print and compare the size with the mail limit. Gmail allows 25 MB per message for personal accounts. |
| Upload a scan to a portal with a size cap | 4, then one step higher | Zoom to 100% on signatures, stamps and handwriting. |
| Keep a contract or invoice that must stay sharp | 1 to 3 | Compare the sizes. These levels do not touch images, so the saving may be small. |
| Share a photo-heavy brochure on a slow connection | 5 or 6 | Look at photos and gradients for blur or blocky areas. |
How to compress a PDF in 3 steps
Add your PDF
Drop one PDF on the box above, or click it to browse. The file card then shows the file name and size.
Set the compression level
Type a number from 1 to 9 in the Compression level field, or keep the starting value of 4.
Run and download
Press Run Compress PDF and wait for the progress bar to finish. Then press Download to save the new file.
Why compress a PDF with indox?
The page does one job and shows you every setting it uses. You get a single control, the compression level, and its label tells you which end keeps quality and which end saves space. You can run one file without creating an account. The file travels over HTTPS, and on the free tier it is deleted automatically within 24 hours after the job finishes. The page is also plain about what it cannot promise. There is no fixed reduction, because the saving depends on what your document contains. When a level alone is not enough, the related tools below remove pages you do not need or split a long file into parts.
- One setting, labeled in plain words
- Upload size shown on the file card
- One file without an account
- Free-tier files removed within 24 hours
- No watermark on the result
What are the limits when you compress a PDF?
- Size
- The free tier has a file size limit. Signing in raises it, and paid plans raise it further.
- Formats
- This tool works on PDF files. To change a file's type, use the PDF converter.
- Privacy
- Files are encrypted in transit and processed on indox infrastructure.
- Deletion
- Free-tier files are deleted automatically within 24 hours after the job finishes. Signed-in output stays in your history for your plan's retention period.
Limits worth knowing
- No reduction is guaranteed. A file that was already optimized may change very little.
- Higher levels give up quality to save space. Look at photos, charts and small print in the result before you delete the original.
- You cannot type a target size such as a mailbox limit. Raise the level one step at a time until the file fits.
- You cannot enter a password here. Remove it from a protected PDF first, then compress the open copy.
- The box takes one file per run. If you drop several at once, only the first is used.
When the result is not what you expected
| What you see | Why | What to do |
|---|---|---|
| The file is barely smaller | It was already optimized, or it is mostly text with few images | Raise the level one step, or drop pages you do not need with Remove Pages. |
| Photos or scans look soft or blocky | From level 4 the images are resized and saved at lower quality | Run the original again at a lower level. A compressed copy cannot get its quality back. |
| It is still over the size limit at level 9 | The content itself is too large for one file | Cut it into parts with Split PDF. |
| The file asks for a password | The page cannot enter a password | Remove it with Unlock PDF, then compress the open copy. |
| The download is the same size or does not open | The file may be damaged, and a failed compression step returns the PDF unchanged | Try Repair PDF, then compress again. |
What do the free and paid plans add?
Free
- All converters
- Daily credit refresh
- Email support
Basic
- Access to all features
- AI Extract
- Priority conversions
- Email support
Highest priority
Premium
- Everything in Basic
- Highest priority queue
- Larger file limits
- Priority support
Pay-As-You-Go
- No subscription
- Credits never expire
- Opt-in auto-refill
- Access to all features
What else can you do with a PDF?
Who compresses PDFs?
People sending attachments
Your mail provider rejects a PDF that is over its attachment limit. A higher level can bring the file under the cap so it goes out as a normal attachment.
Applicants and form fillers
Job, visa and school portals often cap the size of each upload. Compress the scan of your documents until the portal accepts it.
Teams that share reports
A report full of charts and screenshots is heavy to pass around. A lighter copy is easier to post in chat or to download on mobile data.
When to compress a PDF
- An email bounces because the attached PDF is too large.
- An upload form shows a size cap and your file is over it.
- You want a lighter copy of a scanned contract for cloud storage.
- You need to send a brochure or portfolio over a slow connection.
Where can I read more?
Sources
- qpdf manual: command-line optionsqpdf project
- Compress guideStirling-PDF documentation
- Send Gmail messages as attachments, size limitsGoogle Help
Facts checked on October 15, 2026
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Compress PDF FAQs
Which compression level should I choose?
Start with 4, the value the field opens with. If the result is still too large, run the original again at a higher level. If images look rough, drop to a lower one.
How much smaller will my PDF be?
There is no fixed figure. The saving depends on what the document contains, so compare the size on the file card with the size of the download.
Does compression lower the quality?
It can. The level field states that 1 keeps the most quality and 9 makes the smallest file, so quality drops as the number rises. Read the result on screen before you send it.
Can I set an exact target size?
No. The tool accepts a level from 1 to 9 and has no size field. To get under a cap, step the level up and check the download each time.
Can I compress a password-protected PDF?
Not directly. This page does not ask for a password, so take the protection off first and then upload the file.
Why is my downloaded file the same size?
Either the file had little left to squeeze, or the compression step failed and the job returned your PDF as it was. Try a higher level, and if nothing changes, run the job again later.
Do I need an account to compress a PDF?
No, one job runs without signing in. An account and paid plans raise the limits.
When is my file uploaded, and how long is it kept?
The upload starts when you press Run, over an HTTPS connection. On the free tier, indox deletes the file automatically within 24 hours after the job finishes.
What is the Gmail attachment size limit?
Personal Gmail accounts allow 25 MB of attachments per message, according to Google's help page. Work and school accounts follow the limit their administrator sets. If your PDF is over the limit, compress it and check the size of the download.
Why does a scanned PDF look softer after compression?
A scan is a stack of page pictures. From level 4 the tool resizes pictures and saves them again at lower JPEG quality, so scans change more than text pages do. Run the original at a lower level if the result is too rough.