How to Reduce PDF File Size – 5 Free Methods (Windows, Mac, Mobile)

A PDF that is too large to email, too big for a portal, or too slow to open on mobile is one of the most common frustrations in day-to-day document work. The fix is usually straightforward, but the right method depends on your platform and how much reduction you need.

Here are five free methods ranked from fastest to most powerful, covering Windows, Mac, iPhone, Android, and command-line.

Method 1: Browser tool, fastest, works on any device

The ImageAndPDF Compress PDF tool works on Windows, Mac, iPhone, and Android, in any modern browser, no installation or account needed.

1. Go to imageandpdf.com/pdf/compress-pdf
2. Drag and drop your PDF or click to upload
3. The tool compresses and shows the before/after file size
4. Click Download to save the smaller PDF

Need to hit a specific size limit (1 MB, 500 KB, 100 KB)? Use the Compress to Target Size tool instead, it applies progressive compression profiles to reach your target.

Method 2: Re-export from Microsoft Word or PowerPoint

If you have the original source file, re-exporting with optimized settings is the cleanest approach, no quality compromise on text, and you control exactly what resolution images are embedded at.

• Microsoft Word: File → Save As → PDF. In the dialog, choose “Minimum size (publishing online)” under Optimize for. This downsamples images to 150 DPI and subsets fonts, typically cutting the file size by 40–60%.
• Microsoft PowerPoint: File → Export → Create PDF/XPS. Under Options, change Picture quality to “Medium (150 ppi)”from the default “High (220 ppi)”.
• Google Docs / Slides:File → Download → PDF Document. Google automatically optimizes images at a moderate resolution. No quality setting is exposed, but the output is usually smaller than Word's default export.

Method 3: Mac Preview, built-in, no software to install

macOS includes a built-in Quartz filter in Preview that can reduce PDF size without installing anything:

1. Open the PDF in Preview (double-click the file)
2. Go to File → Export as PDF
3. At the bottom of the dialog, click the Quartz Filter dropdown
4. Select “Reduce File Size”
5. Click Save

Important caveat: The default Reduce File Size filter is quite aggressive, it can reduce image quality significantly. Test the output before submitting anything official. For more control, the browser tool or Ghostscript give better results.

Method 4: Ghostscript, maximum control, all platforms

Ghostscript is the professional open-source PDF engine used by most compression services behind the scenes. Install it free at ghostscript.com, then run:

gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 \
  -dPDFSETTINGS=/ebook \
  -dNOPAUSE -dQUIET -dBATCH \
  -sOutputFile=smaller.pdf original.pdf

The -dPDFSETTINGS presets, from most aggressive to least:

• /screen, 72 DPI images, smallest file, on-screen reading only
• /ebook, 150 DPI images, good balance for digital documents
• /printer, 300 DPI, suitable for printing
• /prepress, 300 DPI colour-managed, largest output

For most use cases, start with /ebook. It typically produces 70–85% file reduction while keeping the document clearly legible at normal viewing sizes.

Method 5: iPhone and Android, compress directly from mobile

The browser tool works on mobile too. If you received a large PDF on your phone and need to email or upload it from there:

1. Open Safari (iPhone) or Chrome (Android)
2. Go to imageandpdf.com/pdf/compress-pdf
3. Tap Select PDF, this opens the Files app (iPhone) or Google Drive / local storage (Android)
4. Select the PDF and wait for compression
5. Tap Download, the compressed file saves to your Downloads folder

On iPhone, the downloaded file appears in the Files app under Downloads. From there you can share it directly to Mail, WhatsApp, or any other app via the Share button.

Why is my PDF so large?

Understanding the source of bloat tells you which method will work best:

• High-resolution images: A single 300 DPI photo on an A4 page is 2–4 MB before compression. Presentations and brochures are almost always image-heavy.
• Embedded fonts: Every font family embedded in a PDF adds 200–500 KB. A document using five custom fonts can carry 2+ MB of font data before any content.
• Redundant objects: PDFs that have been merged, edited multiple times, or exported from certain apps accumulate unused objects. Compression removes these automatically.
• Uncompressed scans: A raw scanner output at 300 DPI colour is roughly 25 MB per page. Compression typically gets this to 500 KB–1.5 MB per page at good quality.

When the PDF still will not compress enough

Some image-heavy documents hit a compression floor. If the compressed output is still over your target:

• Convert colour scans to greyscale first. Colour images are 3× the size of greyscale at equal quality. Use the PDF to Greyscale tool, then compress, this often unlocks an additional 50–60% reduction.
• Split into smaller parts. Use our Split PDF tool to divide the document into sections under the size limit and upload separately.
• Use Ghostscript with /screen preset. This gives the absolute smallest file, suitable for reference documents where readability at high zoom is not critical.

Frequently asked questions

How much can a PDF be reduced in size?

It depends on content. Image-heavy PDFs typically reduce by 60–85%. Text-only PDFs reduce by 20–50%. Scanned documents (bitmaps at 300 DPI) usually compress by 70–85%. Some PDFs are already well-optimized and may only reduce by 5–15%.

Will reducing PDF size affect the quality?

For text and vector graphics: no visible quality change at all. For embedded images: slight reduction in sharpness at very high zoom, but imperceptible at normal reading distances. Using “screen” preset on Ghostscript may produce visible degradation, stick to “ebook” for most uses.

Can I reduce PDF size on iPhone or Android?

Yes. The ImageAndPDF Compress PDF tool works on any iPhone or Android in the browser, no app needed. Open the tool in Safari or Chrome, upload, and download the compressed version.

Why is my PDF large even though it only has text?

Text-only PDFs can still be large due to embedded full font files (500 KB–1 MB per font family), redundant objects from merging or editing, or inefficient export settings from the source application. Compression removes these automatically.