How to reuse existing embedded font?

[aeris]

Hello here,

I try to edit an existing PDF with hexapdf. This PDF use embedded font:

page.resources[:Font]

{ :F30 => {
  :Type            => :Font,
  :Subtype         => :Type0,
  :Encoding        => :"Identity-H",
  :BaseFont        => :"EULITT+UbuntuNF",
  :DescendantFonts => #<HexaPDF::PDFArray [0, 0] value=[#<HexaPDF::Reference [16, 0]>]>,
  :ToUnicode       => {
    :Filter => :FlateDecode,
    :Length => 671
  }
}}

I want to reuse this font without loading it again from TTF file on disk, it's not sure to have it.
So I try to reuse this from the PDF file itself, but got stucked

font = page.resources[:Font][:F30]
canvas = page.canvas type: :underlay
canvas.font font

gems/3.4.0/gems/hexapdf-1.4.0/lib/hexapdf/font_loader/from_file.rb:69:in 'File.file?': no implicit conversion of HexaPDF::Type::FontType0 into String (TypeError)

I don't find a way from the doc to reuse such font, is it only possible?

Regard,

[gettalong]

It is generally not possible to re-use a font in this way. The reason for this is that most TrueType and OpenType fonts that are embedded in a PDF have be subset and stripped:

• If a font has been subset, its name is preceeded by "XXXXXX+" where XXXXXX are ascii letters Subsetting means that only the glyphs that are actually shown in the PDF are included in the font. So if, for example, the letter 'Z' is not used in the PDF, its glyph will not be in the subset.
• Furthermore, to reduce the size of the subset font it is possible to strip out font tables that are not needed for an embedded font. One of those tables is the CMAP table which allows a program to get the glyph given a Unicode character.

Nonetheless, if you retrieve a font object from a PDF and the #font_wrapper method returns a non-nil value, this font can be used by HexaPDF. Currently, only fully embedded fonts are usable this way.

PDF viewers and some libraries work around this by looking at the font object and retrieving the same or an equivalent font from the operating system.

[aeris]

Ty for this answer!