How to Compress a PDF for Email (Under 10MB or 25MB)

PDFs that started as Word documents are usually small. PDFs built from scans, photos, or rich graphics balloon fast — a 50-page scanned contract can easily hit 80 MB. Email won’t take it. Forms won’t accept it. The file works fine but it’s just too big.

Compression solves it. Here’s how to do it in your browser, plus what to expect at each compression level.

The fastest way: compress in your browser

Use the PDF Compressor. Drop in your PDF, pick a compression level, click compress, download the smaller version.

The flow:

Open the PDF Compressor
Drag in the PDF
Choose compression level (low / medium / high / extreme)
Click compress
Download the result, sized smaller

Conversion runs in your browser. The PDF never gets uploaded.

What compression levels do

The PDF Compressor works mainly by re-encoding the embedded images at lower quality. Text is already efficiently stored in PDFs and barely shrinks. Images are typically 90%+ of a “big PDF” by file size, so that’s where the savings come from.

Approximate results on a typical scanned PDF:

Level	Quality of embedded images	Size reduction
Low	Near-original, quality ~0.9	20-30%
Medium	Visually identical, quality ~0.8	40-60%
High	Slight softening visible on zoom, quality ~0.6	60-75%
Extreme	Clearly softer images, quality ~0.4	75-90%

Reality varies wildly by source. A PDF built from already-compressed JPGs barely shrinks (the JPGs were already at their compressed size). A PDF built from screenshots or high-quality scans shrinks dramatically.

Recommended setting: start at Medium. Inspect the result. If still too big, go up a level.

Why “medium” is usually right

At Medium compression (image quality ~0.8), the PDF compresses by ~50% with essentially no visible loss. The math: image compression algorithms (JPEG specifically) discard information that the human eye doesn’t easily detect. Quality 0.8 is the sweet spot where invisible-to-the-eye data gets dropped first.

Going below 0.6 (High or Extreme) starts to produce visible “softness” — text scanned from documents looks slightly blurry, fine details in diagrams become muddy. Acceptable for most viewing purposes, but you’d notice on a careful side-by-side comparison.

For an emailable PDF that still looks good, Medium is the right default. For a PDF you just need to share — even if it doesn’t look perfect — go High or Extreme.

Common targets

For Gmail (25 MB limit): aim for under 18 MB to leave room for encoding overhead. Medium compression usually gets there.

For Outlook (20 MB): aim for under 14 MB. Medium or High.

For “must be under 10 MB” forms (common with government, insurance, healthcare uploads): often requires High or Extreme. If still too big, look at splitting (next section).

For “must be under 5 MB” forms: very strict. Extreme compression, and if still too big, the PDF needs structural changes (fewer pages, lower-resolution scans).

When compression isn’t enough: split the PDF

If a 100-page PDF won’t fit even at extreme compression, you can split it into smaller pieces with PDF Splitter. Send each piece as a separate email, or attach to separate form submissions.

Workflow:

Compress the original with PDF Compressor (medium)
Split the compressed PDF with PDF Splitter into 2 or 4 chunks
Each chunk is now much smaller

A 30 MB compressed PDF split into 4 chunks gives you four ~8 MB PDFs — each emailable individually.

When your PDF won’t compress

Sometimes the compressor reports “no significant size reduction.” This happens when:

The PDF is text-only. Text in PDFs is already compact (typically vector representations of fonts). Nothing to compress.
The embedded images were already heavily compressed. A PDF built from JPGs at quality 0.7 has limited room to compress further.
The PDF uses already-efficient encoding like JBIG2 for scanned pages (some advanced PDF producers use this).

In those cases, the path forward is:

Convert PDF to images with PDF to Images
Compress the images with Image Compressor at quality 0.6 or 0.5
Rebuild PDF with JPG to PDF

The round-trip lets you apply aggressive image compression that the PDF compressor alone can’t.

What gets preserved when compressing

PDF compression in our tool is non-destructive for structure — only image data gets re-encoded. So:

Preserved:

All text content (searchable, copyable)
Document structure
Bookmarks and table of contents
Hyperlinks
Form fields
Metadata (title, author, creation date)
OCR text behind scanned pages

Modified:

Embedded images (recompressed at lower quality)
Image embeddings may be downsampled (e.g., 600 DPI image → 300 DPI)

Lost (only at Extreme):

Some color fidelity in images (color profiles simplified)
Fine detail in images at high zoom

For typical use (sending PDFs, archiving, sharing), this is all fine. For specifically print-quality output (sending PDFs to a commercial printer), use Low compression or skip compression entirely.

A 30-second workflow for “this PDF won’t fit in email”

Open PDF Compressor
Drop the PDF in
Medium compression
Click compress
Check the result file size — usually 40-60% smaller
If still too big: re-run with High or Extreme
If still too big: PDF Splitter into 2-3 pieces

Done. Most PDFs fit in email after Medium compression.

What about password-protected or encrypted PDFs?

The PDF Compressor handles password-protected PDFs as long as you can open them. The browser will prompt for the password (or skip — depending on the encryption setup).

PDFs with stronger encryption (certificate-based, AES-256 with restrictions) may resist processing. The compressor doesn’t remove encryption — the output PDF is similarly protected.

For PDFs you can’t open, you can’t compress (no tool can — you need the password). For PDFs that are “view-only” but not strongly encrypted, the compressor usually works.

Privacy

Compression runs in your browser:

The PDF is parsed in JavaScript using pdf-lib
Embedded images are extracted and re-encoded with the same image compression algorithms the Image Compressor uses
The compressed PDF is built in browser memory and offered as a download

Nothing about your PDF touches a server. For sensitive PDFs (medical records, legal contracts, financial statements), this matters — compression keeps the document fully private.

TL;DR

PDF too big for email → PDF Compressor at Medium
Still too big → try High or Extreme
Still too big → PDF Splitter into pieces
Won’t compress at all → PDF → images → compress images → rebuild PDF round-trip
Aim for 18 MB max for safe-cross-provider email
Compression preserves text, links, structure — only image data is re-encoded