How to Reduce PDF File Size — 7 Methods That Work

Why are PDFs so large?

A PDF file size is determined primarily by what it contains. Understanding why your PDF is large helps you choose the most effective method to reduce it.

High-resolution images are the biggest contributor to PDF size. A single photograph from a modern smartphone can be 3–8MB. A PDF containing 10 such photos can easily be 30–80MB before any other content is considered. Even if the images appear small on the page, the full-resolution image data is embedded unless the PDF creator explicitly downsized them.

Scanned documents are images of pages and follow the same logic. A scanner set to 600 DPI creates very large images — one page scanned at 600 DPI in colour can be 15–20MB. Many scanners default to unnecessarily high resolutions for everyday documents.

Embedded fonts add size. When a PDF includes unusual or custom fonts, the font data is embedded inside the file so recipients can view it correctly. A single embedded font can add 100KB–500KB to a file. Documents using many different fonts accumulate this overhead.

Embedded files and attachments add the full size of anything attached to the PDF — spreadsheets, source files, or other documents embedded as attachments.

Unoptimised structure — duplicate objects, orphaned resources, and inefficient cross-reference tables — can add 5–20% to a file without contributing visible content.

Method 1: Use a PDF compressor (fastest, no software needed)

The quickest method for most situations is a browser-based PDF compressor. Our free PDF compressor works entirely in your browser — nothing is uploaded to a server, so sensitive documents stay private.

Upload your PDF, choose a compression level, and download the result. The tool works by re-rendering each page at a lower image resolution and JPEG quality, then rebuilding the PDF. This is most effective on image-heavy PDFs and scanned documents, which are the most common causes of large file sizes. A 20MB scanned document often compresses to 2–5MB using the Balanced setting.

Text-only PDFs will not compress significantly with this method because the text data is already stored efficiently as vectors. For those, see Method 3 below.

Method 2: Reduce resolution before creating the PDF

The best time to control PDF size is before the PDF is created. If you are generating a PDF from a Word document, design application, or any other software, look for "image quality" or "image resolution" settings in the export/save-as-PDF dialog.

For most documents intended for screen viewing and standard office printing, images at 96–150 DPI are perfectly sufficient. You do not need 300 DPI images for a report that will be read on a monitor. In Microsoft Word:

Go to File → Options → Advanced
Scroll to "Image Size and Quality"
Check "Discard editing data" and set resolution to 96 ppi (pixels per inch)
Save the document, then export as PDF

In Adobe Acrobat, when saving as PDF from any application, look for "Smallest File Size" as a preset in the PDF Settings dialog. This applies aggressive image downsampling and compression.

Method 3: Use Print to PDF (for text-heavy documents)

For text-heavy PDFs — reports, articles, books — the "Print to PDF" method often produces the smallest files. Open the PDF in any viewer, press Ctrl+P (Windows) or Cmd+P (Mac), and select "Save as PDF" as the printer. The browser or OS PDF engine creates a fresh PDF from the rendered output, stripping out metadata, unused resources, and structural overhead.

Results vary, but this method commonly reduces text-heavy PDFs by 10–30%. It also flattens any interactive elements (forms, annotations) into the document, which may or may not be desirable.

Method 4: Remove unnecessary pages

If a PDF contains pages you do not need to share — blank pages, appendices, internal draft notes, cover pages — removing them reduces the file size proportionally. Use our free PDF splitter to visually select the pages you want to keep and extract them as a new PDF.

This is especially useful with scanned documents where each page contributes significant size. A 50-page scanned report where you only need 20 pages can be reduced in size by 60% simply by extracting the relevant pages.

Method 5: Reduce scanner resolution

If your large PDF comes from a scanner, the fix is to scan at a lower resolution next time. For documents that will only be read on screen or printed on a standard office printer, 150–200 DPI in colour (or 300 DPI in black and white) is more than sufficient. Many scanners default to 300 or 600 DPI colour, which produces unnecessarily large files for everyday documents.

In greyscale mode rather than colour, file sizes are roughly one-third of the equivalent colour scan. For text-only documents — forms, letters, contracts — scanning in greyscale or black-and-white at 200–300 DPI produces a readable document at a fraction of the size of a full-colour scan.

Method 6: Use PDF/A format for archiving, not sharing

If your goal is long-term archiving rather than sharing, PDF/A format may seem like the right choice — but it is worth knowing that PDF/A files are often larger than standard PDFs, because the standard requires embedding all fonts and prohibits compression techniques that reduce size. Do not use PDF/A if file size reduction is your goal. PDF/A is the right choice for permanent legal or regulatory archiving where format integrity decades into the future is the priority.

Method 7: Use dedicated desktop software for maximum reduction

For the best possible compression on complex PDFs, desktop software outperforms browser-based tools. Adobe Acrobat Pro's "Reduce File Size" and "PDF Optimizer" features can analyse the file, identify opportunities for compression at each component level (images, fonts, streams), and apply the most appropriate method for each.

Ghostscript, a free open-source tool, can achieve excellent compression via the command line:

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

The -dPDFSETTINGS parameter accepts /screen (smallest), /ebook (good balance), /printer, and /prepress (highest quality). For most purposes, /ebook achieves 40–70% size reduction with good visual quality.

Choosing the right method for your situation

Scanned document, too large to email → Use the browser-based compressor (Method 1). Aim for Balanced or Strong depending on how much reduction you need.
PDF with lots of photos → Method 1 (compressor) will work well. Also consider Method 2 if you are recreating the PDF.
Text-only report, slightly too large → Try Method 3 (Print to PDF). It is fast and often removes 10–30% with no quality change.
PDF with unnecessary pages → Method 4 (split and extract). Remove what you don't need before compressing.
Future scans → Method 5 (lower scanner resolution). Fixing the source is always the best long-term solution.
Maximum compression needed → Method 7 (Ghostscript or Acrobat). For very large files or bulk processing, desktop tools give the best results.

How small should a PDF be?

There are no universal rules, but these are practical benchmarks for common situations:

Email attachment — Most email servers accept attachments up to 10–25MB. Some strict corporate systems limit to 5MB. Aim for under 5MB for reliable delivery.
Online form upload — Government and institutional portals often limit PDF uploads to 2–10MB. Check the specific limit before submitting.
Website download — For PDFs linked from a website, under 5MB is ideal for users on mobile connections. Over 10MB will cause noticeable download delays on slower connections.
Print shop submission — For commercial printing, larger is often better — print shops need high-resolution images. Do not compress a PDF that will be professionally printed.