Limitations

Rendering is lenient and it says so: content pdfboss cannot read is skipped so the rest of the page still rasterizes, and every dropped or approximated item lands in a report. pdfboss render warns on stderr, the terminal explorer raises a notice, and the libraries return it through render_page_reporting (Rust) and Page.render_reporting() (Python). See Rendering pages for the reporting APIs.

The whole not-yet-supported list is two faces: /Symbol and /ZapfDingbats have no license-clean substitute, so they stay blank rather than borrowing an unrelated face's glyphs.

Fonts

Glyph painting is staged in tiers (embedded-only, all-embedded, full) selected with --fonts (CLI), the fonts parameter (Python) or RenderOptions::glyph_painting (Rust); the tiers are described in Rendering pages. What stays limited:

• full substitutes only non-embedded simple fonts, and a bold sans substitute is not visually distinct from regular weight.
• Standard-14 advance widths come from the Adobe Core-14 AFM tables when a substitute is used, behind the PDF's own /Widths.

CMaps and CID fonts

Type0 /Encoding CMaps resolve: the predefined ISO 32000 Table 118 CJK set is compiled in (behind the predefined-cmaps feature, on by default in the CLI and the wheel), embedded CMap streams parse the same way, widths key on the mapped CID, vertical text (WMode 1) advances by /W2//DW2 with the default position vector, and extraction maps CIDs to Unicode through the character collection when /ToUnicode is absent.

Deferred: vertical runs still extract as horizontal-schema spans, one per show operator, with x/y at the glyph origin.

JBIG2

JBIG2Decode covers the embedded stream format end to end: generic regions (all four templates, with TPGDON, arithmetic or MMR-coded), symbol dictionaries and text regions in both the arithmetic and the Huffman variant (refinement/aggregate-coded symbols and refined instance placements included), pattern dictionaries and halftone regions, generic refinement regions (both templates, with TPGRON) refining either the page or a retained intermediate region, intermediate regions of every type, and custom code table segments. Nothing in the standard's segment type table is refused; a malformed or truncated stream fails with a message naming what was wrong instead of rendering a blank.

Colour

Colour converts to sRGB. ICCBased spaces parse their embedded profile (v2 and v4; matrix/TRC and grayTRC models, and A2B0 lookup pipelines): a profile equivalent to sRGB keeps the exact device-RGB path, others transform per colour with Bradford adaptation from the D50 connection space, and a profile that will not parse falls back to the /N channel-count reduction. CalRGB, CalGray, and Lab convert through CIE XYZ the same way.

Only a profile's default transform is used (rendering intents are not switched), and DeviceN keeps a tint approximation.

JPEG 2000

JPXDecode implements ITU-T T.800 (JPEG 2000 Part 1); what it approximates it reports as a render warning rather than passing off silently.

ICC profiles embedded in the JPEG 2000 container are interpreted through the same ICC engine as ICCBased colour (a profile equivalent to sRGB or device gray keeps the exact device path, others transform per sample), and only a profile that will not parse falls back to the channel-count approximation. sYCC converts with the exact IEC 61966-2-1 Amd. 1 inverse.

Part 2 (ISO/IEC 15444-2) extensions are tolerated in the container but not decoded. Every output sample is normalized to 8 bits per channel with round-to-nearest, so sources deeper than 8 bits (the spec allows up to 38) still land on an 8-bit output grid.

Optional content

Optional content groups (PDF layers, ISO 32000 §8.11) are honored per the document's default configuration: rendering and text extraction skip layers it turns off, counting them on the reports' hidden counters.