Tutorials · 12 min read
How to Compress a PDF for Free: Online, Mac, Windows, iPhone and Open-Source Tools
Free ways to make a PDF smaller for email or an upload form, what each method does to quality, and what to try when the file is still too big.
By AIToolBase Editorial Team · Published
Short answer: For a quick, free result, upload the PDF to an online compressor such as Adobe Acrobat online, iLovePDF or Smallpdf, pick a compression level and download the smaller file. On a Mac, open the PDF in Preview, choose File > Export, set Quartz Filter to Reduce File Size and save. If the file is private (an ID card, a bank statement, a medical report), use an offline method instead: Preview on Mac, re-exporting from Office when you have the original document, or the free open-source tool Ghostscript on any computer.
What you should pick depends on why you are compressing:
- To email or share a large file: any of the online tools at a medium ("recommended") level usually does the job.
- To get under an upload limit such as 1 MB or 500 KB: you need to reduce image resolution, and sometimes switch to grayscale or split the file. See hitting an exact size target.
- To shrink without any visible change: use lossless optimisation (qpdf), but expect a smaller saving.
This guide is for students, job applicants and office workers who keep running into "file too large" errors. It covers why PDFs get big, free online and offline methods for each device, privacy, and fixes for when compression goes wrong.
Why some PDFs are so big
A PDF is a container. Its size comes mostly from what is inside:
- Images and photos. A single high-resolution photo can weigh more than hundreds of pages of text.
- Scans. A scanned PDF is a picture of every page. A 20-page scan at high resolution is really 20 large images.
- Embedded fonts. PDFs carry their fonts so they look the same everywhere. This adds some weight, but usually far less than images.
- Leftovers. Files edited many times, or exported by some apps, can contain unused objects and uncompressed data.
Lossy vs lossless compression
This is what "compress PDF without losing quality" really depends on.
- Lossless compression reorganises and re-packs the file's data without changing what you see. Every pixel and letter stays identical. The saving is usually modest, and on a file full of photos it may be small.
- Lossy compression lowers image resolution (downsampling) and/or recompresses images as lower-quality JPEGs. This is where the big savings come from, and it is also why photos can turn blurry or blocky.
Text and vector graphics (charts, logos drawn in the PDF) normally stay sharp under lossy compression because they are not images. The exception is a scanned PDF, where the text is an image, so heavy compression can make it hard to read.
In our view: if a file is mostly text, almost any compressor at a medium level will keep it looking the same. If it is mostly photos or scans, decide how much image quality you can give up, and always open the result before sending it.
Online: Adobe Acrobat, iLovePDF and Smallpdf
All three work in a browser on any device, including phones. Here is what their official pages say, as of November 2026.
| Tool | Compression levels | Free use, per the official page | What happens to your file |
|---|---|---|---|
| Adobe Acrobat online | High, Medium, Low | "Free with limited use"; files up to 2 GB; no sign-up needed for basic compression, sign-in to save or share | Deleted from Adobe's servers unless you sign in to save it |
| iLovePDF | Extreme, Recommended, Less compression | Free plan: 2 files and 200 MB per Compress task; "limited document processing" | Kept for a maximum of 2 hours, then removed; you can delete it yourself after processing |
| Smallpdf | Basic (free), Moderate and Strong (Pro) | No sign-up needed; "usage limits may apply" | Automatically deleted after one hour |
The steps are almost identical on all three:
- Open the tool's Compress PDF page (Adobe, iLovePDF, Smallpdf).
- Drag in your PDF or click the upload button.
- Choose a compression level. Start with the middle option (Adobe's Medium, iLovePDF's Recommended). On Smallpdf's free tier, only Basic is available.
- Download the compressed file and open it to check the quality.
Kevin Stratvert's short tutorial walks through both online tools and desktop applications for shrinking a PDF:
Uploading means a copy of your document sits on someone else's server, even if only for an hour or two. The deletion promises above come from each company's own pages and you cannot check them yourself. For passports, Aadhaar or national ID cards, bank statements, payslips, tax forms or medical records, use an offline method below, or read the service's privacy policy first and decide whether you are comfortable with it.
On a Mac: Preview's Reduce File Size filter
Preview is built into macOS and works offline. According to Apple's Preview guide:
- Open the PDF in Preview.
- Choose File > Export.
- In the Quartz Filter pop-up menu, choose Reduce File Size.
- Click Save. To keep the original, enter a new name in Export As before saving.
Apple's guide also lists manual options in the Export dialog on current macOS versions: Optimize images for screen and Save images as JPEG, plus Create Linearized PDF (which is for fast web viewing, not for making the file smaller). Apple warns that "the PDF may be of lower quality than the original."
In our view: the Reduce File Size filter is aggressive. On a photo-heavy or scanned PDF it can make images noticeably blurry, so zoom in on the exported copy before you delete anything. If the result is too rough, try an online tool's medium level or Ghostscript's /ebook preset (see below), which give you more control.
On Windows: what free built-in options actually work
Windows has no built-in "compress PDF" button. These are the free options that are documented:
- Re-export from Office when you have the original file. Microsoft's PDF guide says that in Excel, PowerPoint, Access and Visio, after choosing **PDF (\.pdf) in the Save as type list, you can select Minimum size (publishing online)* "if file size is more important than print quality." Microsoft's steps for Word do not mention this option, so check whether your version's Save As dialog shows it.
- Shrink the pictures first. In Word, PowerPoint and Excel, select a picture, go to Picture Format > Compress Pictures, choose a lower Resolution, and untick Apply only to this picture to change every image. Then save as PDF again. Microsoft notes the default picture resolution in Microsoft 365 is 220 ppi.
- Use Ghostscript for a PDF you did not create. It runs on Windows too (see below).
We found no Microsoft documentation saying that printing to Microsoft Print to PDF reduces file size, so don't rely on it for compression.
On iPhone and Android
Apple does not document a built-in way to reduce a PDF's size on iPhone. The Compress option in the Files app creates a ZIP archive, which is a different thing: the PDF inside is unchanged, and a ZIP file often isn't accepted by upload forms anyway. Some third-party guides describe a Shortcuts action for optimizing PDF size, but we could not confirm it on an Apple support page, so treat it as something to try rather than a guaranteed method.
On Android, we did not find an official built-in PDF compressor either.
The practical option on both phones is to open one of the online tools above in your mobile browser, upload the file from Files or your downloads, and save the result. The same privacy warning applies. For sensitive documents, wait until you are at a computer and use an offline method.
Free open-source tools: Ghostscript, qpdf and Stirling-PDF
These run on your own computer, so your file never leaves it. They take a few minutes to set up but give the most control.
Ghostscript: real, lossy compression
Ghostscript is a long-running open-source PDF and PostScript engine, available under the GNU AGPLv3 (with commercial licences from Artifex). Its pdfwrite device rewrites the PDF and can downsample images using presets:
| Preset | What the Ghostscript docs say | Color/gray image resolution |
|---|---|---|
/screen | Low-resolution output, like Distiller's "Screen Optimized" | 72 dpi |
/ebook | Medium-resolution output, like Distiller's "eBook" | 150 dpi |
/printer | Like Distiller's "Print Optimized" (no downsampling by default) | 300 dpi |
/prepress | Like Distiller's "Prepress Optimized" (no downsampling by default) | 300 dpi |
A good first try is the /ebook preset:
gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -dBATCH -dNOPAUSE -sOutputFile=smaller.pdf input.pdfOn Windows, the command-line program is called gswin64c (or gswin32c) instead of gs. If the result is still too large, switch to /screen. To also convert everything to grayscale, which helps a lot with colour scans of black-and-white documents, add -sColorConversionStrategy=Gray:
gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -sColorConversionStrategy=Gray -dBATCH -dNOPAUSE -sOutputFile=smaller-gray.pdf input.pdfThe Ghostscript docs note that the best quality, closest to the input, comes from not setting PDFSETTINGS at all, so use the presets only when you actually need a smaller file.
qpdf and pikepdf: lossless clean-up
qpdf is a "content-preserving" PDF transformer. Its manual says it "will not resample images or make optimizations that modify content." It can still make some files smaller by packing objects into compressed object streams and recompressing data:
qpdf --object-streams=generate --recompress-flate --compression-level=9 input.pdf smaller.pdf--object-streams=generatecreates object streams and compresses objects where possible.--recompress-flatedecompresses and recompresses existing Flate (zip-style) data, and--compression-level=9uses the strongest level.
This is the closest thing to "compress PDF without losing quality," but because it leaves images alone, the saving on a photo-heavy file is often small. qpdf also has an --optimize-images option that converts non-JPEG images to JPEG when that is smaller; the manual points out that JPEG is lossy, so that option is no longer fully lossless.
If you work in Python, pikepdf is a library built on qpdf. Its Pdf.save() method exposes the same ideas, for example object_stream_mode=pikepdf.ObjectStreamMode.generate and recompress_flate=True. You can browse more free document tools in our productivity category.
Stirling-PDF: a self-hosted toolbox
Stirling-PDF is a web app with 50+ PDF tools, including compress, that you can run yourself with Docker or as a desktop client. Its README describes it as "open-core" and says you can edit PDFs "without sending documents to external services." Check its LICENSE file to see which features are open source.
Hitting an exact size target (1 MB, 500 KB, 2 MB)
Upload portals for job applications, exams and government forms often set limits like 2 MB, 1 MB or under 500 KB. No tool can promise an exact size, because the result depends on what is in the file. Work through these in order and check the size after each step:
| Target / situation | Approach to try |
|---|---|
| A little over the limit (e.g. 2.4 MB to under 2 MB) | Online tool at the medium level, Preview's Reduce File Size, or Ghostscript /ebook |
| Under 1 MB from a photo-heavy or scanned file | Ghostscript /screen or iLovePDF's Extreme compression, then check readability |
| Under 500 KB for a scanned form or certificate | Grayscale plus /screen or /ebook; or rescan at a lower resolution in black-and-white/grayscale |
| One page is huge, the rest are small | Replace or re-export that one page (often a photo) at lower resolution |
| Many pages, strict per-file limit | Split the PDF into parts if the form accepts several files, or upload only the pages asked for |
| You have the original Word/PowerPoint file | Compress pictures in Office, then save as PDF again |
If you are scanning paper yourself, the cheapest fix is at the scanning stage. Scanning a text document in grayscale or black-and-white at a moderate resolution produces a far smaller file than a full-colour, high-resolution scan, and the text usually stays readable. Check your scanner app's settings before scanning.
Troubleshooting
| Problem | Likely cause | What to do |
|---|---|---|
| Still too big after compressing | The file is mostly large images and the tool used a light setting | Use a stronger level, Ghostscript /screen, grayscale, or split the file |
| Text looks blurry | It is a scanned PDF, so the text is an image and was downsampled | Use a gentler level (/ebook instead of /screen), or rescan in grayscale |
| Photos are blocky or smeared | Strong JPEG recompression | Go back to the original and use a medium level |
| The file got bigger | The PDF was already well compressed, or an option like linearization added data | Keep the original; pikepdf's docs note linearized files tend to be larger |
| Online tool fails or asks to pay | Free tier limits (file size, files per task, or levels reserved for paid plans) | Try another tool, or use Preview or Ghostscript offline |
| Fillable form fields or signatures stopped working | Rewriting the PDF can change form or signature data | Compress before signing, or ask the recipient whether a larger file is acceptable |
| Need an editable copy instead | Compression keeps the PDF format | See how to convert a PDF to Word for free |
Frequently Asked Questions
What is the best way to compress a PDF for free?
For non-sensitive files, an online tool such as Adobe Acrobat online, iLovePDF or Smallpdf is the quickest. For private documents, use Preview on a Mac or Ghostscript on any computer, since the file stays on your device.
Can I compress a PDF online free with no sign-up?
Yes. As of November 2026, Smallpdf's page says no sign-up is needed, and Adobe's page says basic compression needs no sign-up (you sign in only to save or share). Each service applies its own usage limits.
How do I compress a PDF without losing quality?
Use lossless optimisation such as qpdf, which does not resample images, or a light setting like iLovePDF's "Less compression." Truly lossless methods usually save less space, especially on scanned or photo-heavy files.
How do I compress a PDF to under 1 MB or 500 KB for free?
Reduce image resolution with a strong setting (Ghostscript /screen, iLovePDF's Extreme), convert to grayscale, and remove pages you don't need. For scans, rescanning in grayscale at a lower resolution is often the most reliable way to get under 500 KB.
How do I compress a PDF on Mac?
Open it in Preview, choose File > Export, set Quartz Filter to Reduce File Size, and save under a new name. Check image quality afterwards, because Apple warns the result may be lower quality.
How do I compress a PDF on iPhone?
Apple does not document a built-in PDF compressor on iPhone, and the Files app's Compress option only makes a ZIP. Use an online compressor in Safari for non-sensitive files, or compress on a computer.
How do I compress a PDF for free on Windows?
If you have the original Office file, compress its pictures and save as PDF again, choosing Minimum size where your app offers it. For any existing PDF, use an online tool or the free Ghostscript command line.
How do I compress a PDF in Adobe Acrobat?
Adobe's free online tool at adobe.com/acrobat/online/compress-pdf.html lets you upload a PDF, choose High, Medium or Low compression and download the result. Unlimited and batch compression require a paid plan.
Is iLovePDF compress PDF safe?
iLovePDF's FAQ says files are kept for a maximum of 2 hours and then removed, and you can delete them yourself after processing. That is the company's own promise, so avoid uploading highly sensitive documents to any online tool.
Sources
- Adobe: Compress PDF online
- iLovePDF: Compress PDF, FAQ and pricing
- Smallpdf: Compress PDF
- Apple Support: Compress a PDF in Preview on Mac
- Apple Support: Create or open ZIP files on iPhone and iPad
- Microsoft Support: Save or convert to PDF in Office desktop apps
- Microsoft Support: Reduce the file size of a picture
- Ghostscript documentation: High-level devices (pdfwrite and PDFSETTINGS) and Using Ghostscript
- Artifex: Licensing
- qpdf manual: Running qpdf
- pikepdf API reference
- Stirling-PDF on GitHub
Reviewed on November 3, 2026. Free limits, compression level names and file-retention policies of online tools change often, and Apple and Microsoft menus can differ between versions, so check the linked official pages before relying on a specific limit.