Why can a PDF look blurry after Preview compression?

Image compression can lower the detail in scanned pages and embedded pictures. Text stored as vector objects differs from text that is part of a scanned image. Inspect the export rather than assuming every document is affected the same way.

How can I compress a PDF on Mac in a browser?

Add an unencrypted PDF to the tool below. Start with Gentle and default advanced settings for structural cleanup; try a stronger preset if you accept recompression of large JPEG images. Download and inspect the result. Source documents are processed locally.

Why is my compressed PDF still too large?

Already optimized documents may have little structural redundancy, and stronger modes only recompress eligible image streams. A smaller size is not guaranteed. Compare the actual result; for a large scan, a better source scan can help more than repeated compression.

What PDF size should I target for email?

Use the recipient or provider’s published attachment limit and leave margin for message overhead. No single file size guarantees delivery through every mail gateway.

How to Compress a PDF on Mac

Learn how to compress a PDF on Mac with Preview or a local browser tool. Follow export steps, compare methods, and check text and images before sharing.

How to reduce PDF size in Mac Preview

Mac Preview can reduce a PDF without installing an app. Try its export workflow on a copy, then inspect the result. For another approach, the local browser tool below offers structural cleanup or image recompression. Neither method guarantees a smaller file or unchanged appearance.

Open a copy in Preview
Keep the original PDF, then open the document in the Preview app.
Choose File → Export
Use Export to create a separate PDF rather than overwriting your original.
Select Quartz Filter → Reduce File Size
Choose the filter in the export dialog. Available export options vary with macOS version.
Save with a new name and inspect it
Compare file size, page count, small text, and images before using the compressed copy.

Apple notes that compression can lower quality. Some versions also offer screen-image optimization and JPEG export options. If the result is unsuitable, keep the original or try the local tool below.

Apple’s Preview compression guide Try local PDF compression below

100% Local · Files Never Leave Your Device

Compression Mode

or drag & drop here

Paste from clipboard with Cmd+V · Multiple files supported

Supported: PDF

No server upload limit0 KB uploadNo watermark100% Free

Processing happens locally in your browser — nothing is uploaded.

Try a sample:

Never uploaded
No watermark
No sign-up
No server upload limits

How It Works

Simple 3-step compression powered entirely by your local browser

§ 01

Step 01

Add Your PDF

Select or drop the PDF from your device.

§ 02

Step 02

Choose a Compression Mode

Gentle focuses on structure; stronger modes may recompress large embedded images.

§ 03

Step 03

Download the Result

Review the new file size and output quality before using the compressed PDF.

Why Choose LessMB

The private, modern alternative to legacy cloud compressor websites

100% In-Browser Privacy

Zero bytes uploaded. Your personal photos, sensitive documents, and private videos never touch external servers or cloud storage.

Zero Queue & Instant Start

No waiting in cloud conversion queues or watching slow upload bars. Processing starts the millisecond you drop your file.

Hardware Acceleration

Harnesses WebAssembly SIMD and WebCodecs GPU encoding for high-fidelity compression directly on modern consumer hardware.

No Credit Consumption

Free tier compression uses your own device compute, meaning zero server credit drain for everyday single and batch tasks.

Choose a PDF Compression Method

Choose by document type and check the exported copy.

Method	Approach	Verified
Mac Preview Built-in export A quick built-in method. File size and image quality depend on the selected options; inspect the exported copy.	Quartz Filter / export options	Apple guide checked 2026-10-07
LessMB Gentle With default advanced settings, Gentle does not resample images. Already optimized documents may not shrink much.	Structural cleanup	Current PDF engine
LessMB Balanced / Strong / Extreme May resize and recompress large embedded JPEG images while keeping vector text objects. Scanned text can lose detail; not every image stream is recompressed.	Image recompression	Current PDF engine

Tips for Best Results

For text-based PDFs, start with Gentle and leave image overrides unset. Rewriting the structure can help, but an efficient PDF may barely change.
For image-heavy PDFs or scans, compare a stronger preset at full zoom. Scanned text is part of an image, so resampling can affect legibility.
Open the downloaded copy, check all pages, try selecting existing text, and compare diagrams or small print. This compressor does not add OCR to scans.
Keep originals of digitally signed documents and interactive forms. Rewriting a PDF can affect signatures or document features; check the copy in the intended reader.
Encrypted or password-protected PDFs are not supported by this workflow. Start with a permitted, unencrypted copy.

Frequently Asked Questions

Straight answers about this tool and how it works

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Tutorials & Guides

Deep dives from the LessMB editorial team

How to Compress a PDF Online Without Guesswork

See how PDF structure cleanup and image recompression affect file size, when stronger modes may reduce image quality, and how to choose the right mode.

Read guide