What Affects PDF Quality?
When converting Word to PDF, three main factors determine the output quality and file size:
- Image compression: How photographs and graphics embedded in your document are compressed in the PDF output.
- Font embedding: Whether and how fonts are included in the PDF to ensure consistent rendering on all devices.
- Resolution (DPI): The pixel density of embedded images, which determines sharpness when printed or zoomed.
Important: Text in PDF is always vector-based and remains perfectly sharp at any zoom level. Quality settings primarily affect images and photographs embedded in your document, not the text itself.
Image Compression in PDFs
Images are typically the largest component of a PDF file. The compression method and level you choose dramatically affect both quality and file size.
JPEG Compression
Best for photographs and complex images with gradients. JPEG is lossy — it discards some visual information to achieve smaller files. Quality levels:
- Maximum (95%): Virtually indistinguishable from the original. Large files.
- High (85%): Excellent quality. Artifacts invisible at normal viewing distance. Good for printing.
- Medium (75%): Good quality for screen viewing. Minor artifacts visible when zooming. Ideal for email and web.
- Low (50%): Noticeable quality loss. Only for maximum file size reduction.
ZIP/Flate Compression
Lossless compression that preserves every pixel. Best for screenshots, diagrams, text-heavy images, and graphics with sharp edges. File sizes are larger than JPEG for photographs but smaller for simple graphics.
| Image Type | Best Compression | Why |
|---|---|---|
| Photographs | JPEG (85%) | Natural images compress well with JPEG |
| Screenshots | ZIP/Flate | Sharp edges blur with JPEG |
| Charts/Graphs | ZIP/Flate | Clean lines and text need lossless |
| Logos | ZIP/Flate | Preserves crisp edges and solid colors |
| Scanned pages | JPEG (85-95%) | Scanner noise makes lossless inefficient |
Font Embedding Options
Font embedding ensures your document looks the same on every device, even if the recipient does not have your fonts installed.
Full Font Embedding
Includes the complete font file in the PDF. Every character in the font is available, allowing recipients to edit the PDF and add new text using the embedded font. The downside is file size: a single font family can add 200–500 KB to the PDF.
Subset Font Embedding
Includes only the characters actually used in the document. If your document uses letters A through Z but not the Greek alphabet, only the Latin characters are embedded. This reduces font data by 50–90% compared to full embedding.
| Embedding Type | Typical Size per Font | Editable? | Best For |
|---|---|---|---|
| No embedding | 0 KB | N/A (font substitution) | Never recommended |
| Subset | 20–80 KB | Limited (existing chars only) | Most documents |
| Full | 200–500 KB | Yes (all characters) | Editable PDFs, forms |
Best practice: Use subset embedding for final documents that will not be edited. Use full embedding only for PDF forms or documents that recipients need to modify.
Resolution Settings for Embedded Images
Image resolution (DPI) determines how sharp images appear when printed. Screen viewing is less sensitive to DPI because monitors display at fixed pixel dimensions.
| Use Case | Recommended DPI | Typical File Size (10-page doc) |
|---|---|---|
| Email / Web sharing | 96–150 DPI | 500 KB – 2 MB |
| Office printing | 200–300 DPI | 2–8 MB |
| Professional printing | 300–600 DPI | 8–30 MB |
| Maximum quality / Archival | 600 DPI | 20–50+ MB |
Image downsampling reduces the DPI of images that exceed the target resolution. For example, if your Word document contains a 600 DPI photo and you set the target to 300 DPI, the image is downsampled to 300 DPI during conversion, reducing file size while maintaining print quality.
Recommended Settings by Use Case
- Web / Email (smallest file): JPEG compression at 75%, subset font embedding, 150 DPI images. Produces compact PDFs under 2 MB for most documents.
- Office printing (balanced): JPEG compression at 85%, subset fonts, 300 DPI images. Good quality for laser printers with reasonable file sizes.
- Professional print (high quality): JPEG at 95% or ZIP compression, full font embedding, 300–600 DPI. Maximum quality for commercial printing.
- Archival (maximum quality): ZIP compression (lossless), full font embedding, 600 DPI, PDF/A compliance. Largest files but guaranteed quality preservation.