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Set an entry in an attachment's /Params dictionary

Source: R/attachment_authoring.R
pdf_attachment_set_dict_value.Rd

Writes a string-valued entry in the attachment's parameter dictionary. Common keys:

Usage

pdf_attachment_set_dict_value(att, key, value)

Arguments

att

A pdfium_attachment from pdf_attachments() or pdf_attachment_new(). Parent doc must be readwrite.

key

The dictionary key as a non-empty character scalar.

value

The string value as a character scalar; UTF-8 accepted.

Value

Invisibly returns the parent pdfium_doc.

Details

  • "Desc" — a human-readable description.

  • "AFRelationship" — the AF/EF relationship type ("Source", "Data", "Alternative", etc.).

  • "ModDate" — modification date as a PDF date string (see pdf_parse_date() for the format).

Wraps FPDFAttachment_SetStringValue, which writes into the attachment's /Params subdictionary. Mirrors pdf_attachment_dict_value() on the read side.

Ordering: PDFium's FPDFAttachment_SetStringValue requires the attachment's /Params dictionary to already exist. Call pdf_attachment_set_data() first on any attachment that doesn't have one yet (the file data write auto-creates /Params, populating Size, CreationDate, and CheckSum); only then can you append further keys with this function. On a fresh attachment from pdf_attachment_new() this means the natural sequence is pdf_attachment_new() → pdf_attachment_set_data() → pdf_attachment_set_dict_value().

Not exposed: the file stream's own /Subtype entry (the MIME type returned by pdf_attachment_mime_type()) lives on the attachment's embedded file stream, not on /Params, and PDFium has no public setter for it. Passing key = "Subtype" here writes /Params/Subtype, which won't be picked up by pdf_attachment_mime_type(). See dev/upstream-patches/ for the upstream gap.

Encoding: PDFium's FPDFAttachment_SetStringValue stores the value as a PDF byte-string interpreted in PDFDocEncoding on read. ASCII round-trips cleanly; non-ASCII Unicode characters are lossy through the read path (the bytes are written but FPDFAttachment_GetStringValue's GetUnicodeText step misinterprets multi-byte UTF-8 sequences as PDFDocEncoding bytes). This is a PDFium-side inconsistency — FPDFAnnot_SetStringValue uses the wide-string-aware CPDF_String path and round-trips Unicode correctly. Until upstream is fixed, restrict attachment-dict values to ASCII when round-trip fidelity matters.

See also

pdf_attachment_dict_value().