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Embedded fonts in Ruby

To extract embedded fonts in a document.

def obj_is_embedded_font(indirect_obj)
  if indirect_obj.IsFree() then
    return false
  elsif !indirect_obj.IsDict() && !indirect_obj.IsStream() then
    return false
  end

  type_obj = indirect_obj.FindObj("Type")
  if type_obj.nil? || !type_obj.IsName() then 
    return false
  end

  type_name = type_obj.GetName()
  if type_name != "Font" then
    return false
  end

  subtype_obj = indirect_obj.FindObj("Subtype")
  if !subtype_obj.nil? && subtype_obj.IsName() then
    subtype_name = subtype_obj.GetName()
    if subtype_name =="CIDFontType0" then
      return false
    end
  end

  font = Font.new(indirect_obj)
  return font.IsEmbedded()

end

doc = PDFDoc.new(filename)
sdfdoc = doc.GetSDFDoc()
for i in 1..sdfdoc.XRefSize() do
  indirect_obj = sdfdoc.GetObj(i)
  if obj_is_embedded_font(indirect_obj) then
    # perform document processing
  end
end

linkAbout embedded fonts

PDF documents access fonts from one of two places: the host machine rendering the PDF document or from within the PDF document itself. When a font is used in a PDF document which is not available on the machine loading that document and it's not embedded within the document the viewer will usually load a different font. When that font is contained within the PDF document itself we call that an embedded font. When a PDF contains an embedded font that font can still be rendered even if it is not defined on the host machine.

All font information in a PDF is stored in the SDF layer as an SDF object and exists as either a dictionary or a stream. When a font exists a dictionary that means that means that it is defined exclusively within the PDF document but if it is defined as a stream that means it exists as a file which may or may not exist within the PDF document itself. It is possible for either type to be embedded.

It's also possible to programatically embed fonts within a PDF with the PDFTron SDK. You can find an example in the ElementBuilder sample code.

The samples below demonstrates how to iterate over all embedded fonts found within a PDF document. Note that because this requires several low-level operations additional care must be taken for to check for possible null pointers. Also note that fonts with the subtype CIDFontType0 are not not counted as embedded fonts because they are necessarily referenced by a parent font within the same document.

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