How to Compress PDF File Size Free Online

Last Updated: September 2026

A PDF that's too large causes real problems: email services reject attachments over 10–25MB, file upload fields on websites often cap at 5–10MB, and large PDFs eat mobile data when shared on WhatsApp or Slack. Compressing a PDF reduces its file size so it uploads, sends, and opens faster — without changing the actual content.

This guide covers four free methods. The right one depends on how much reduction you need and what software you have.

Method 1: Docuvory — Free Online Compressor (Recommended)

No installation required. Works on any device — Windows, Mac, iPhone, Android.

Go to Docuvory's Compress PDF tool.
Click "Select PDF Files" or drag your file into the upload area.
Click "Process". The tool automatically analyses the file and applies optimal compression settings.
When complete, click "Download File".

The tool typically achieves 40–80% file size reduction on PDFs that contain scanned images or high-resolution photos. PDFs that are already mostly text see smaller gains (10–30%), because text data compresses very efficiently already.

Security: Your file is encrypted in transit and permanently deleted from our servers within 1 hour of processing. We never retain document content.

Method 2: Adobe Acrobat Pro

Acrobat Pro gives you granular control over exactly how much each element is compressed.

Open your PDF in Acrobat Pro.
Go to File → Save As Other → Optimized PDF (or in newer versions: Tools → Optimize PDF).
In the PDF Optimizer dialog, you can adjust:
- Images — set JPEG quality (lower = smaller), resolution (72 DPI for web, 150 DPI for general use, 300 DPI for print)
- Fonts — subsetting embedded fonts removes unused characters
- Transparency — flatten transparent layers
- Discard Objects — remove comments, form fields, hidden layers
- Clean Up — remove invalid bookmarks, unused named destinations
Click OK → choose a save location.

For quick results without configuration, use File → Reduce File Size (or Save As Other → Reduced Size PDF) — this applies Acrobat's automatic settings.

Method 3: Ghostscript (Maximum Compression, Command Line)

Ghostscript is a free, open-source tool that produces the highest compression ratios available — often 60–90% smaller than the original. It requires running a command in your terminal, so it's best suited to technical users or IT professionals.

After installing Ghostscript (ghostscript.com), run this command:

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

PDFSETTINGS quality levels (from smallest to highest quality):

/screen — 72 DPI images, smallest size, for on-screen reading only
/ebook — 150 DPI images, good balance for sharing and email
/printer — 300 DPI, suitable for printing
/prepress — 300 DPI + colour preservation, for professional print production

For most sharing purposes, /ebook gives the best size-to-quality trade-off.

Note: We mention Ghostscript for completeness but don't recommend it for general users — the command line is a barrier, and for typical needs the Docuvory tool produces very similar results with zero configuration.

Method 4: Other Free Online Tools

Several other online PDF compressors are available: Smallpdf, ilovepdf, and PDF24. All work similarly to Docuvory. Key differences to be aware of:

File size limits — free tiers often cap at 5–10MB per file
Daily limits — some cap the number of free compressions per day
Data retention — check each tool's privacy policy; retention periods vary
Account requirements — some require email registration for free use

Docuvory has no file count limit, no registration required, and automatically deletes files within 1 hour.

Why Is My PDF Still Large After Compressing?

This is the most common question after using a compressor. Here are the real reasons:

1. The PDF is a scanned document with uncompressed images

Scanners often produce very high-resolution images (600 DPI or more) embedded in PDFs. Compression works by reducing this resolution and re-encoding the images. A 50MB scanned PDF can often be reduced to 3–5MB. If your compressed result is still large, try compressing again with a lower quality setting, or use Ghostscript with /screen settings.

2. The PDF contains embedded fonts with full character sets

Some PDFs embed an entire font library (including every character the font supports, even characters not used in the document). Subsetting the font — keeping only the characters actually used — can save several MB. Adobe Acrobat's Optimise PDF handles this automatically.

3. The PDF has embedded 3D objects, videos, or interactive elements

PDFs can contain embedded multimedia. Compression tools generally cannot compress these elements. To shrink such files, the multimedia must be removed from the PDF in an editor first.

4. The PDF is already well-compressed

A text-only PDF with no images may be 200KB already — there is little left to compress. Compression tools work by removing redundancy and reducing image quality; if both are already minimal, the savings are minimal too.

5. You need to remove pages, not compress

If some pages are image-heavy and others are not, removing the heavy pages entirely (rather than compressing them) often produces much smaller results. Use Remove PDF Pages first, then compress.

Comparison Table

Method	Typical Reduction	Requires Install?	Technical Skill	Cost
Docuvory	40–80% for image-heavy PDFs	No	None	Free
Adobe Acrobat Pro	40–75%, precise control	Yes	Low	$19.99/month
Ghostscript	60–90% (highest possible)	Yes	Medium	Free
Other online tools	30–70%	No	None	Free (with limits)

Frequently Asked Questions

Will compressing a PDF reduce quality?

It depends on the content. For PDFs that contain only text, compression is lossless — the output is visually identical to the input. For PDFs with images, compression reduces image resolution and quality. For most on-screen viewing and general sharing, the quality difference is imperceptible. If the PDF will be commercially printed, use Acrobat Pro with the /printer or /prepress setting.

How do I compress a PDF to under 1MB for email?

Use Docuvory's Compress PDF first. If the result is still over 1MB, check how many pages the PDF has — removing unnecessary pages with Remove PDF Pages before compressing often achieves the target size when compression alone can't.

Can I compress a PDF on my phone?

Yes. Docuvory works in any mobile browser. No app needed.

Does compressing a PDF change the page dimensions?

No. Page size (A4, Letter, etc.) is not affected by compression. Only the internal data (images, fonts, embedded objects) is reduced.

My PDF is password-protected. Can I compress it?

You need to remove the password first. Use Docuvory's Unlock PDF, then compress.

Related Tools

Compress PDF — reduce PDF file size online
Remove PDF Pages — delete pages to reduce size
Compress Images — compress JPG and PNG files
Unlock PDF — remove password before compressing

How to Compress a PDF File to Make It Smaller (4 Free Methods)