poppler would use a font named "Symbol" even if it has nothing to do
with PostScript standard Symbol font. At least one such incompatible
font is seen in the wild, so there's a real danger of a bogus
substitution. (The issue can be easily fixed by fiddling with fontconfig
configuration. However, I believe that this is poppler's responsibility
to choose proper substitutes for standard Type 1 fonts.)
$ ls -l /etc/fonts/conf.d/
total 28
lrwxrwxrwx 1 root root 38 Nov 29 11:22 10-autohint.conf -> /etc/fonts/conf.avail/10-autohint.conf
lrwxrwxrwx 1 root root 13 Oct 6 2008 10-debconf-autohint.conf -> autohint.conf
lrwxrwxrwx 1 root root 39 Nov 29 11:22 20-fix-globaladvance.conf -> ../conf.avail/20-fix-globaladvance.conf
lrwxrwxrwx 1 root root 39 Nov 29 11:22 20-unhint-small-vera.conf -> ../conf.avail/20-unhint-small-vera.conf
lrwxrwxrwx 1 root root 39 Nov 29 11:22 30-defoma.conf -> /var/lib/defoma/fontconfig.d/fonts.conf
lrwxrwxrwx 1 root root 36 Nov 29 11:22 30-metric-aliases.conf -> ../conf.avail/30-metric-aliases.conf
lrwxrwxrwx 1 root root 33 Nov 29 11:22 30-urw-aliases.conf -> ../conf.avail/30-urw-aliases.conf
lrwxrwxrwx 1 root root 30 Nov 29 11:22 40-nonlatin.conf -> ../conf.avail/40-nonlatin.conf
lrwxrwxrwx 1 root root 27 Nov 29 11:22 45-latin.conf -> ../conf.avail/45-latin.conf
lrwxrwxrwx 1 root root 31 Nov 29 11:22 49-sansserif.conf -> ../conf.avail/49-sansserif.conf
lrwxrwxrwx 1 root root 37 May 5 22:56 50-enable-terminus.conf -> ../conf.avail/50-enable-terminus.conf
lrwxrwxrwx 1 root root 26 Nov 29 11:22 50-user.conf -> ../conf.avail/50-user.conf
lrwxrwxrwx 1 root root 27 Nov 29 11:22 51-local.conf -> ../conf.avail/51-local.conf
lrwxrwxrwx 1 root root 27 Nov 29 11:22 60-latin.conf -> ../conf.avail/60-latin.conf
lrwxrwxrwx 1 root root 35 Nov 29 11:22 65-fonts-persian.conf -> ../conf.avail/65-fonts-persian.conf
lrwxrwxrwx 1 root root 30 Nov 29 11:22 65-nonlatin.conf -> ../conf.avail/65-nonlatin.conf
lrwxrwxrwx 1 root root 29 Nov 29 11:22 69-unifont.conf -> ../conf.avail/69-unifont.conf
lrwxrwxrwx 1 root root 40 Nov 29 11:22 70-no-bitmaps.conf -> /etc/fonts/conf.avail/70-no-bitmaps.conf
lrwxrwxrwx 1 root root 31 Nov 29 11:22 80-delicious.conf -> ../conf.avail/80-delicious.conf
lrwxrwxrwx 1 root root 31 Nov 29 11:22 90-synthetic.conf -> ../conf.avail/90-synthetic.conf
-rw-r--r-- 1 root root 959 Jun 1 2008 README
-rw-r--r-- 1 root root 250 Feb 21 15:42 autohint.conf
-rw-r--r-- 1 root root 306 Apr 1 2006 no-bitmaps.conf
-rw-r--r-- 1 root root 257 Apr 1 2006 no-sub-pixel.conf
-rw-r--r-- 1 root root 256 Apr 1 2006 sub-pixel.conf
-rw-r--r-- 1 root root 247 Apr 1 2006 unhinted.conf
-rw-r--r-- 1 root root 296 Apr 1 2006 yes-bitmaps.conf
$ pdffonts delta.pdf
name type emb sub uni object ID
------------------------------------ ----------------- --- --- --- ---------
Symbol Type 1 no no no 4 0
$ rm -Rf ~/.fonts/
$ fc-match Symbol
s050000l.pfb: "Standard Symbols L" "Regular"
$ pdftoppm delta.pdf > delta-ok.ppm
$ mkdir ~/.fonts
$ cp /path/to/windows-xp/c:/windows/fonts/symbol.ttf ~/.fonts/
$ fc-match Symbol
symbol.ttf: "Symbol" "Regular"
$ pdftoppm delta.pdf > delta-bogus.ppm