accpdf

Experiments with creating accessible PDFs from Pandoc, see Pandoc #5409.

• Running make pdf in a document subdirectory, e.g. tagged-pres should produce a tagged PDF/A-2a file using Lualatex via Pandoc, from the markdown sources in the directory and the Pandoc templates and Lua filters in the common directory. The pdfnb target removes empty lines created by RawBlock in Pandoc from the generated .tex file (which can create superfluous vertical space in the PDF) and runs the result through Lualatex. This target also uses a workaround to avoid duplicating tagging commands with the longtable package, which Pandoc uses for tables.
• The tag structure in the resulting PDF can be inspected using the Poppler pdfinfo utility, e.g. pdfinfo -struct-text tagged-pres.pdf.
• The file can be validated as PDF/A using veraPDF, e.g. ~/verapdf/verapdf tagged-pres.pdf. Use the latest version of veraPDF.