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.
or drag & drop here
Paste from clipboard with Cmd+V · Multiple files supported
Supported: PDF
- Never uploaded
- No watermark
- No sign-up
- No server upload limits
How It Works
Simple 3-step compression powered entirely by your local browser
Select or Drop Images
Choose single or multiple JPG, PNG, WebP, AVIF, HEIC files. Your files remain 100% on your device.
Adjust Slider or Target Size
Fine-tune quality with the smart compression slider or specify exact target KB/MB for Discord or email.
Instant Download
Processed in milliseconds via WebAssembly codecs. Download individual images or pack all into a ZIP archive.
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 |
Macプレビューの「ファイルサイズを縮小」の問題点と解決策
macOSの「プレビュー」アプリで「ファイルサイズを縮小」フィルタを適用すると、画像が強制的に低解像度（72 DPI）にリサンプルされ、文字や図面が極端にぼやけてしまいます。LessMBはブラウザ上でベクター文字を保護しつつ、適切なDPIで最適化します。
| 指標 | LessMB (ブラウザ内処理) | macOS Preview (純正フィルタ) | ColorSync (ColorSync調整) |
|---|---|---|---|
| 画像解像度 | 150 DPI / 96 DPI 選択可能 | 強制 72 DPI (極度にぼやける) | 設定可能 (XML編集が必要) |
| ベクター文字 | 100% ベクター品質維持 | 文字は保持も背景画質劣化 | ベクター保持 |
| 目標サイズの指定 | 目標MB/KB直接入力 | 指定不可（縮小率の予測不能） | 容量指定不可 |
| 操作の手軽さ | ドラッグ＆ドロップのみ | 書き出しメニューから | 難解（ColorSyncユーティリティ設定） |
Macでよく扱う3種類のPDF実測データ（縮小率と視認性）
| 文書種別 | 元のサイズ | プレビュー圧縮後 | LessMB 圧縮後 | 文字の可読性 |
|---|---|---|---|---|
| 領収書・請求書スキャン | 12.4 MB | 1.1 MB (印鑑読取不可) | 2.4 MB (高精細) | 提出合格 |
| Keynote発表スライド | 38.2 MB | 4.2 MB (グラフ劣化) | 8.5 MB (ベクター維持) | Retina対応 |
| LaTeX論文・数式 | 6.8 MB | 3.9 MB | 1.8 MB | 数式完璧 |
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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