What a free PDF compressor limits: size, levels, uploads
A free PDF compressor is limited by the largest file it takes, the levels it gives away, and whether it uploads your PDF. Most comparison articles rank these tools by how small the output gets instead. That is the wrong axis, because the reduction depends mainly on the PDF itself.
The largest PDF file each online compressor accepts
The first limit is the size of the file you can hand over. Adobe is the only one of the four server-based vendors that prints a number on its compress page, and the number is 2GB. Smallpdf says usage limits may apply without saying what they are, and iLovePDF publishes no free cap on the page at all.
For a one-page form this never matters. It starts to matter with a long scanned report, where a quiet cap turns into an error message halfway through the upload.
Which compression levels are free: often not the strongest
The second limit is how hard you are allowed to squeeze. Most tools offer three levels, from a light pass that leaves images alone to a strong one that shrinks and recompresses them. Not every tool gives all three away.
Smallpdf keeps Moderate and Strong for paying users, so the free level is its lightest. Adobe offers all three levels free but reserves batch processing and advanced settings for a paid Acrobat plan. iLovePDF, PDF24 and sakuttoAI give every level to free users.
Whether the PDF compressor uploads your file
The third limit is not a number: it is where your PDF goes. Adobe, Smallpdf, iLovePDF and PDF24 all receive the file on their servers, compress it there and send it back. Smallpdf and PDF24 say they delete it after one hour; Adobe says it deletes files automatically.
A deletion policy is a promise about what happens after the upload, not a way to avoid it. For a contract, a payslip or a medical record, the question is whether the file leaves your device in the first place.
Note that usage limits may apply, and our “Moderate” and “Strong” compression are Pro features. ／ Your PDFs are secured with TLS encryption, comply with GDPR, and are ISO/IEC 27001-certified. For extra peace of mind, we automatically delete files after one hour.View official source →— from smallpdf.com
Free PDF compressor comparison of five online tools
Only one of the five tools keeps your PDF on your device, and only one publishes a free size cap. The rest leave the size question open or answer it with "no limits".
Free limits and file handling in five PDF compressors
| Tool | Largest file | Free levels | Your file |
|---|---|---|---|
| sakuttoAI | Your device's memory | 3 + advanced | Never uploaded |
| Adobe Acrobat online | 2GB | 3 | Deleted automatically |
| Smallpdf | Not published | 1 of 3 | Deleted after one hour |
| iLovePDF | Not published | 3 | Not stated on the page |
| PDF24 | No limits stated | Adjustable | Deleted after one hour |
Read the PDF compressor table from the file column first
Start with the Your file column on the right. If that column rules a tool out for your document, the size and level columns do not matter. Next, check the file size column against your PDF, and only then look at which levels you get.
Figures come from each vendor's own compress page, checked on September 28, 2026. Free limits change, so look at the live page before planning a large job around one of them.
No compression ratio per tool: the PDF decides it
A "percent smaller" figure per tool would mislead. The same tool can shrink one PDF by 90% and another by almost nothing, depending on whether the pages are photos or plain text. Adobe says as much: mostly-text files compress less because text is already compact.
A ranking built on one test file would tell you about that file, not about yours. The honest comparison is the three limits above, then a trial on your own PDF.
Files that are comprised of mostly text compress less dramatically since text data is already compact.View official source →— from adobe.com
Compress PDF online with Adobe, Smallpdf, iLovePDF and PDF24
All four upload your PDF to their servers; what differs is how much they let you do for free. From the outside they work the same way: you drop a PDF on the page, their server compresses it, and you download the result.
Adobe compress PDF accepts files up to 2GB
Adobe Acrobat's online compressor takes files up to 2GB, the highest published free cap among the five tools. You choose High, Medium or Low, and Adobe describes the tool as free with limited use.
Batch processing, unlimited use and the finer settings sit behind a paid Acrobat plan. If you have one very large file, Adobe is the safe choice; if you have forty small ones, the free tier will feel narrow.
Adobe's PDF compressor can handle files up to 2GB, so you can reduce the size of those large PDFs. ／ You can choose between High, Medium, and Low compression level in Acrobat's online tool, balancing your needs for quality and size. ／ Unlimited compression, batch processing, and advanced setting controls require a paid Acrobat plan.View official source →— from adobe.com
Smallpdf compress keeps two of its three levels for Pro
Smallpdf's free level is Basic; Moderate and Strong are Pro features. That makes it a good fit when a light pass is enough, and a poor one when you need to push a scan under a strict upload limit.
On security, Smallpdf lists TLS encryption, GDPR compliance and ISO/IEC 27001 certification, and deletes files after one hour. It also warns that usage limits may apply to free use, without giving a number.
iLovePDF compress offers three levels with no published cap
iLovePDF gives free users all three of its levels. Each one is labeled with its trade-off between quality and size, so you can pick one without thinking about DPI.
The compress page does not publish a free size or file-count limit, so you find out only when you hit it. Files can come from your computer or from Google Drive, and they are processed on iLovePDF's servers.
Extreme Compression ／ Less quality, high compression ／ Recommended Compression ／ Good quality, good compression ／ Less compression ／ High quality, less compressionView official source →— from ilovepdf.com
PDF24 compress: free, no limits, deleted after one hour
PDF24 is free, needs no registration and states no usage limits. Advertising pays for it. It also has the most controls of the four, including image quality, DPI and a lossless mode that leaves images untouched but saves little.
Files travel over SSL to servers in Germany and are deleted after one hour. The page's line about the tool running "on your system" means it works on any operating system, not that the PDF stays on your computer.
No registration required ／ Servers are located in Germany ／ Files are automatically deleted from the PDF24 server after one hourView official source →— from tools.pdf24.org
Reduce PDF size in the browser without uploading the file
sakuttoAI opens and rewrites the PDF inside your browser, so no copy is sent to a server. Its figures are the developer's own measurements, like every vendor figure in "Free limits and file handling in five PDF compressors".
What each sakuttoAI compression level does to a PDF
Low barely shrinks the file: it removes metadata and tidies the internal structure but leaves every image as it was. Standard, the default, redraws each embedded image at half its width and height and saves it as JPEG. High goes further on both size and JPEG quality.
In sakuttoAI's own measurements, Standard made image-heavy PDFs around 60–90% smaller and High around 70–90%. A PDF of plain text shrank by about 1% at every level, which is the same pattern Adobe describes. Advanced settings let you set image quality and DPI yourself, or turn images grayscale.
The free plan covers three tasks a day across all tools
Free accounts get three tasks a day in total across every sakuttoAI file tool. Pro is unlimited.
Signing in takes an email link or a Google account, with no password to create. The first run of a tool you have not used before does not count toward the three.
There is no service-side size cap because nothing is uploaded; the practical limit is your device's memory. Results download one by one or together as a ZIP, and you can compress a PDF the same way in a phone browser as on a computer.
Which free PDF compressor to pick: your strictest limit
Pick the tool by the strictest limit your file runs into, not by compression quality. Confidential files, very large scans and text-only PDFs each point to a different choice.
Confidential PDF: use a compressor that never uploads
If the document must not leave your device, pick a browser-based tool such as sakuttoAI. Deletion after an hour, encryption in transit and certifications all describe what happens to a copy you have already sent. Not sending it is a different category of safety.
Very large PDF file: Adobe has the highest free cap
For a scan in the hundreds of megabytes, rely on Adobe's 2GB cap. The other server-based tools publish no number, and a browser tool is bounded by your device's memory, which a phone may run out of first.
Text-only PDF: no online compressor will shrink it much
A PDF made of text is already compact, so no tool cuts it by much. If a text-only file is still too large, the weight usually comes from embedded fonts or a few images, and re-exporting from the original document often helps more than any compressor.
FAQ
- Is it safe to use a free PDF compressor?
- It depends on where the file goes. Adobe, Smallpdf, iLovePDF and PDF24 all upload your PDF to their servers; Smallpdf and PDF24 say they delete it after one hour. If the document must not leave your computer, use a tool that processes it in the browser, such as sakuttoAI.
- Does compressing a PDF lower its quality?
- Only where images are re-encoded. Stronger levels shrink and recompress the pictures inside the PDF, so photos and scans lose some detail while the text stays sharp. A lossless setting leaves images alone, and the file gets only a little smaller.
- Which free tool handles the largest PDF?
- Adobe Acrobat's online compressor, which accepts files up to 2GB. The other server-based tools here do not publish a size cap as a number, so for a very large scan Adobe is the one you can plan around.
- Can I compress a PDF without signing up?
- Yes. PDF24 states that no registration is required. sakuttoAI asks for a free sign-in with an email link or Google, with no password, and gives three tasks a day in return.
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