#!/bin/bash

WATERMARK_TEXT="VOTRE TEXTE À WATERMARKER"
COLOR="red"
INPUT_PDF="$1"
OUTPUT_PNGs="./pdf"
WATERMARK_SIZE=50
WATERMARK_PNG_SIZE="800x300"

convert -size ${WATERMARK_PNG_SIZE} xc:white -font Arial -pointsize ${WATERMARK_SIZE} \
          -gravity NorthWest -draw "fill ${COLOR} text 70,15  '${WATERMARK_TEXT}'" \
          -gravity SouthEast -draw "fill ${COLOR} text 70,150  '${WATERMARK_TEXT}'" \
          stamp.png

pdftoppm ${INPUT_PDF} ${OUTPUT_PNGs} -png

for pic in *.png; do
    if [ ${pic} != "stamp.png" ]; then
        composite -dissolve 25% -tile stamp.png ${pic} ${pic//.png}-marked.png
    fi
done

convert *-marked.png ${INPUT_PDF}-out.pdf
rm *.png