In order to use a font other than the standard 14 with -add-text, it
must be added to the file. The font source PDF is given, together with the
font's resource name on a given page, and that font is copied to all the pages
in the input file's range, and then written to the output file.
The font is named in the output file with it's basefont name, so it can be
easily used with -add-text.
For example, if the file fromfile.pdf has a font /GHLIGA+c128 with
the name /F10 on page 1 (this information can be found with
-list-fonts), the following would copy the font to the file
in.pdf on all pages, writing the output to out.pdf:
Text in this font can then be added by giving -font /GHLIGA+c128. Be
aware that due to the vagaries of PDF font handling concerning which characters
are present in the source font, not all characters may be available, or the
encoding (mapping from input codes to glyphs) may be non-obvious.