Diff between two PDFs. Crude, but useful for revisions. Requires wdiff and pdftotext. See diff.sh for usage.

cwdiff

#!/bin/sh

# Use this instead of diff[1] to get colored[2] word-based diffs.
# Useful for text documents that have reflowed paragraphs.
# Requires that wdiff is installed in your $PATH.
#
# [1] All diff options are ignored. Only replaces simplest usage.
# [2] Colors are always emitted. If piping into less, use "-R" or set LESS=-R

# Iain Murray, February 2009, Tweaked in June 2011

if [ "$#" -lt 2 ] ; then
    echo 'Usage: cwdiff FILE1 FILE2'
    echo '       cwdiff [any options will be discarded] FILE1 FILE2'
    echo
    echo 'cwdiff emits colored, word-based diffs. Requires wdiff(1).'
    echo 'If piping into less use -R option or set LESS=-R'
    echo
    exit
fi

# Discard any options, for example SVN attempts to set a bunch of GNU diff
# options
shift $(($# - 2))

# Color commands adapted from cdiff alias by
# Paul Warren <pdw@ex-parrot.com> 12/01/2001
# http://ex-parrot.com/pdw/cdiff.html
#  colour for added lines (bright blue)
#  (yellow, used in cdiff, alias is less robust to terminal background colour)
diffnew=`tput setf 1``tput bold`
#  colour for removed lines (bright red)
diffold=`tput setf 4``tput bold`
#  reset - original pair, unset all attributes
reset=`tput op``tput sgr0`


# The -3 option to wdiff gives no context, so I'm getting wdiff to spit out the
# whole document and using grep to trim it down. The regex for grep could be
# improved, but for text documents is probably ok, and at worst will include
# some extra output that can be ignored..
wdiff \
    --start-delete "${diffold}[-" \
    --end-delete "-]${reset}" \
    --start-insert "${diffnew}{+" \
    --end-insert "+}${reset}" \
    -n "$1" "$2" \
    | grep -C2 '\['
# CAREFUL: The line above contains an escape character.
# Don't copy the grep command by typing ^[ instead of 

# This grep line hits false positives more often for me:
# | grep -C2 '[{[][-+].*[-+][]}]'

cwdiff2

#! /bin/bash

# Copyright (C) 2009-2015 Christoph Junghans
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#
#version 0.1    04.08.10 -- initial version
#version 0.1.1, 05.08.10 -- added -D and -o
#version 0.1.2, 04.10.10 -- make -D work again and better help
#version 0.1.3, 10.05.11 -- added --text to diff_opts to allow diff of binary files (issue #3)
#version 0.1.4, 10.05.11 -- removed --text again and handle case of binary files
#version 0.2.0, 15.04.12 -- clean up + bugfix thanks to Arne
#version 0.2.1, 15.04.12 -- clean up + new bug report address
#version 0.2.2, 20.04.12 -- fixed a bug if argument were dirs
#version 0.2.3, 18.12.12 -- replace usage of mktemp with bash built-ins
#version 0.2.4, 31.08.13 -- fixed deleted leading spaces
#version 0.2.5, 06.09.13 -- do not expand escape sequences in diff
#version 0.2.6, 18.09.13 -- allow 1st argument begin a file with --filter
#version 0.2.7, 09.03.15 -- included a patch from NetBSD
#version 0.2.8, 13.03.15 -- moved issue tracker to github 
#version 0.3.0, 15.03.15 -- print help2man compliant help and version
#version 0.3.1, 30.06.15 -- fix --diffopts option (fixes #4) 
#version 0.3.2, 12.11.15 -- make output processable by less -r/-R
#version 0.4.0, 12.11.15 -- dropped a2ps and out option, clean up

FAT_GREEN=""
GREEN=""
FAT_RED=""
RED="" #also used as indicator
MAGENTA=""
FAT_BLACK=""
OFF=""
NL="
"

usage="Usage: ${0##*/} [OPTIONS] FILE1 FILE2"
diff="no"
filter=
diff_opts='--new-file --unified --show-c-function --recursive'
ab=

color_filter() {
  #use RED as an indicator if colors are on
  if [[ ${RED} ]]; then
    sed -e "s/\[-/$RED/g" -e "s/-\]/$OFF/g" -e "s/{+/$GREEN/g" -e "s/+}/$OFF/g" $1
  else
    cat $1
  fi
}

die() {
  [[ $* ]] && echo "$*"
  exit 1
}

show_help () {
  cat << eof
A colorized version of (w)diff, which can be used a wrapper script, too.
$usage

Options:
 -f, --filter         Act as a wdiff color filter only and don't execute diff/wdiff
                      internally, just colorize input (no ARGS = read from stdin)
 -d, --diff           Preprocess input with diff and before giving it to wdiff
                      (very useful for dirs). Option can be used in combination
                      with --filter option meaning input is a patch.
 -D, --diffonly       Process input with diff, but NOT with wdiff, so ${0##*/}
                      basically acts like a colorized version of diff. Option
                      can be used in combination with --filter option meaning
                      input is a patch.
     --diffopts XXX   Change options given to diff. The default is '$diff_opts'.
     --ab             Replace common trunc of dirname by 'a' and 'b'
     --no-color       Disable color
     --               Stop parsing options
 -h, --help           Show this help
 -v, --version        Show version

Examples:
 ${0##*/} -d dir1 dir2                     Compare two directories
 ${0##*/} file1 file2                      Compare two files
 ${0##*/} --ab -D dir1 dir2                VCS like output from compaing two directories
 wdiff file1 file2 | ${0##*/} -f           Colorize the output of wdiff
 diff -u file1 file2 | ${0##*/} -D -f      Colorize the output of diff

Report bugs and comments at https://github.com/junghans/cwdiff/issues or junghans@votca.org
eof
}

shopt -s extglob
while [[ ${1} = -?* ]]; do
  if [[ ${1} = --??*=* ]]; then # case --xx=yy
    set -- "${1%%=*}" "${1#*=}" "${@:2}" # --xx=yy to --xx yy
  elif [[ ${1} = -[^-]?* ]]; then # case -xy split
    if [[ ${1} = -[o]* ]]; then #short opts with arguments
       set -- "${1:0:2}" "${1:2}" "${@:2}" # -xy to -x y
    else #short opts without arguments
       set -- "${1:0:2}" "-${1:2}" "${@:2}" # -xy to -x -y
    fi
  fi
  case $1 in
   --ab)
    ab="yes"
    shift;;
   --no-color)
    unset FAT_GREEN GREEN FAT_RED RED MAGENTA OFF FAT_BLACK
    shift;;
   -f | --filter)
    filter="yes"
    shift ;;
   -d | --diff)
    diff="yes"
    shift ;;
   -D | --diffonly)
    diff="only"
    shift ;;
   --diffopts)
    diff_opts="$2"
    shift 2;;
   -h | --help)
    show_help
    exit 0;;
   --vcs)
    echo "${0##*/}: $(sed -ne 's/^#version.* -- \(.*$\)/\1/p' $0 | sed -n '$p')"
    exit 0;;
   -v | --version)
    cat << eov
${0##*/} $(sed -ne 's/^#version \(.*\) -- .*$/\1/p' "$0" | sed -n '$p')

$(sed -ne 's/^# \(Copyright.*\)/\1/p' "$0")
This is free software: you are free to change and redistribute it.
License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl2.html>
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Written by C. Junghans <junghans@votca.org>
eov
    exit 0;;
   --)
    shift
    break;;
  *)
   die "Unknown option '$1'";;
  esac
done

[[ $1 = - ]] && filter="yes" && shift
if [[ ! $filter ]]; then
  [[ ! $1 || ! $2 ]]  && die "Please specify two files/dirs or add --filter option"
  #use -e as it could be file or dir
  [[ -e $1 ]] || die "Could not read file/dir '$1'"
  [[ -e $2 ]] || die "Could not read file/dir '$2'"
  [[ $3 ]] && die "I don't know what to do with arguments '${@:3}'"
else
  [[ -n $1 && ! -f $1 ]] && die "Could not read file '$1'"
  [[ $2 ]] && die "I don't know what to do with arguments '$*' together --filter option"
fi

if [[ $diff != no ]]; then
  if [[ ! $filter ]]; then
    exec 3< <(diff $diff_opts "$1" "$2")
    #don't die here, because diff of binary files give exit code = 2
  else
    [[ $1 ]] && exec 3<$1 || exec 3<&0
  fi
  # don't do this if we have not files ;-)
  if [[ $ab && $1 && $2 ]]; then
    #find the longest equal part in $1 and $2 from the end
    for ((i=1;i<=(${#1}<${#2}?${#1}:${#2});i++)); do
      [[ ${1:0-$i} != ${2:0-$i} ]] && break
    done
    ((i--))
    a="${1:0:${#1}-$i}"
    b="${2:0:${#2}-$i}"
  else
    a=a; b=b
  fi
  # -r to not expand escape sequences in diff
  while read -r -u 3; do
    #small trick, because "read -u 3 i" would split the line and
    #leading space would be lost.
    i="${REPLY}"
    if [[ $i = "Files "*" and "*" differ" ]]; then # binary case
      i="${i/$a/a}"
      i="${i/$b/b}"
      echo "$i"
    elif [[ $i = diff* ]]; then # diff header line
      i="${i/ $diff_opts}"
      i="${i/$a/a}"
      echo "$FAT_BLACK${i/$b/b}$OFF"
    elif [[ $i = ---* ]]; then
      echo "${FAT_RED}${i/$a/a}${OFF}"
    elif [[ $i = +++* ]]; then
      echo "${FAT_GREEN}${i/$b/b}${OFF}"
    elif [[ $i = @@* ]]; then
      echo "${MAGENTA}${i}${OFF}"
    elif [[ $i = -* ]]; then
      [[ $diff = only ]] && echo "${RED}${i}${OFF}" || t1+="${i#-}$NL"
    elif [[ $i = +* ]]; then
      [[ $diff = only ]] && echo "${GREEN}${i}${OFF}" || t2+="${i#+}$NL"
    else
      # only true for diff != only
      # cut the last newline do avoid an empty line at the end (echo append newline)
      # echo -n would also work, but wdiff has strange behaviour if the 2nd file is
      # empty, it will not append newline, which make the output look strange
      [[ $t1 || $t2 ]] && { wdiff ${RED:+-n} <(echo "${t1%$NL}") <(echo "${t2%$NL}") | color_filter; }
      t1=
      t2=
      [[ $diff = only ]] && echo "${i}" || echo "${i## }"
    fi
  done
  # thanks to Arne Babenhauserheide for pointing out this case is missing
  # if there was + or - lines at the end, which has not been printed yet
  [[ $t1 || $t2 ]] && { wdiff ${RED:+-n} <(echo "${t1%$NL}") <(echo "${t2%$NL}") | color_filter; }
elif [[ $filter ]]; then
  color_filter $1
else
  wdiff ${RED:+-n} "$1" "$2" | color_filter
fi

diff.sh

# sample usage
# cwdiff gives {+added+} and {-removed-} in highlighted text
# cwdiff2 gives add words in green and removed words in red
pdftotext old.pdf old.txt
pdftotext new.pdf new.txt
cwdiff old.txt new.txt > diff.txt
less -N diff.txt