Read the document's file identifier from its trailer

Returns the raw bytes of the PDF trailer's /ID entry. The identifier is a two-element array [permanent, changing]: permanent is a hash that should stay constant across saves of the same logical document; changing is updated each time the file is rewritten. Use id_type = "permanent" (the default) to track document identity, or "changing" to detect that the file has been re-saved.

Usage

pdf_doc_file_id(doc, id_type = c("permanent", "changing"), password = NULL)

Arguments

doc

A pdfium_doc from pdf_doc_open(), or a character path.

id_type

One of "permanent" (default) or "changing".

password

Optional password for encrypted PDFs when doc is a path. Ignored when doc is already an open pdfium_doc.

Value

A raw vector. Zero-length when the document has no /ID entry.

Details

Wraps FPDF_GetFileIdentifier. The identifier is binary; PDF writers conventionally produce 16-byte MD5 hashes but the length is unspecified and PDFs from non-standard writers may return any byte string (or none at all).

Examples

fixture <- system.file("extdata", "fixtures", "shapes.pdf",
  package = "pdfium"
)
if (nzchar(fixture)) pdf_doc_file_id(fixture)
#> raw(0)