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Package cmap reads the codes of composite fonts: which bytes of a string make up one code, and which character identifier (CID) each code selects (PDF 2.0 9.7.5).

Package cms reads the signed data of the Cryptographic Message Syntax (RFC 5652, PKCS #7) as far as PDF signatures use it, and checks it: the digest of what was signed against the signed attributes, the signature against the signer's certificate.

Package cmyk converts DeviceCMYK to sRGB as a press would print it, through a SWOP press profile, as PDFium, MuPDF, Poppler and Ghostscript convert through profiles of their own, instead of the naive formula R = (1-C)(1-K).

Package content scans PDF content streams without allocating per operand.

Package corpus fetches the public test corpus and writes synthetic technical-drawing pages.

Package pdfedit puts edited documents together: the page tree, the catalogue, pages of the edited document with everything around them and pages imported from others alone (ADR 0013).

Package pdffont is the PDF side of a font: not its outlines, which are the font program's business, but what the document says about reading a string of bytes with it — which codes the string holds, how wide each is, what each glyph is called and what text it stands for (ADR 0012).

Package pdfsyntax holds the lexical rules of the PDF object syntax that both the file reader (internal/pdf) and the content stream scanner (internal/content) need: character classes, numbers and the escapes of names and strings.

Package pdfwrite writes PDF files made of objects built in memory and of objects copied from source documents.

Package stdfont holds the stand-ins for the standard fonts Symbol and ZapfDingbats, which have alphabets of their own: subsets of DejaVu Sans (Bitstream Vera licence, see LICENSE-DejaVu) with their character sets, and Adobe's metrics and built-in encodings for them.

Package testpdf builds small PDF files for tests: a sample with the structures editing must keep or drop, and an encrypted one.