A document is only as robust as its embedded typography. If a PDF references a font that is not installed on the viewing machine, the PDF reader will silently substitute a fallback font (typically Arial or Times New Roman), destroying the layout and paginating differently.
The Mechanics of Embedding
When a PDF engine embeds a font, it extracts the TrueType (TTF) or OpenType (OTF) binary and injects it directly into the PDF object stream. This guarantees visual fidelity.
Subsetting: The Size Solution
Full font files, particularly CJK (Chinese, Japanese, Korean) fonts, can exceed 10MB. Embedding a full font for a two-page document is highly inefficient. Subsetting analyzes the document text, extracts only the utilized glyphs (e.g., 'a', 'b', 'c', '1'), and creates a custom, miniature font dictionary containing only those characters.
Licensing Restrictions (FsType)
Fonts contain a metadata flag called fsType (Embedding Licensing Rights). An engine respecting these flags may refuse to embed a font if the foundry has marked it as 'Restricted License' or 'Preview & Print Only', forcing a rasterization fallback.