Summary Overview
How embedding only the characters used in a document reduces file sizes and prevents font conflicts.
What is Font Subsetting?
When you embed a font in a PDF, you have two choices:
- Fully Embed: Include the entire font file, containing thousands of characters for dozens of languages, including characters you did not use.
- Subset Embed: Include only the specific characters used in your document (e.g. if your text is “Hello”, the PDF only contains vectors for ‘H’, ‘e’, ‘l’, and ‘o’).
Subsetting is standard practice in modern prepress workflows.
The Print Risk: Bloated Files and Character Mappings
While fully embedding fonts ensures all characters are available, it has drawbacks:
- Large File Sizes: Large OpenType fonts can be several megabytes. If your document uses multiple fonts, the PDF size grows quickly, causing slow uploads and processing times on print servers.
- Licensing Violations: Some font creators prohibit full embedding to prevent users from extracting the font file from the PDF.
- Font Conflicts: When multiple PDFs are combined (imposed) onto a single print sheet, fully embedded fonts with matching names can conflict, causing characters to render incorrectly.
How Filecheck Manages Font Subsets
Filecheck inspects all embedded font tables within the PDF:
- Subset Analysis: We check if the font is flagged as a subset (indicated by a 6-letter prefix tag in the PostScript name, e.g.
ABCDEF+Helvetica). - Size Optimization: If full fonts are detected, Filecheck flags a warning or automatically down-subsets the fonts using our serverless PDF optimization library.
- Speed and Security: This reduces file sizes by up to 80%, speeding up cloud storage transfers and ensuring secure, conflict-free layouts on high-volume presses.