Batch PDF Watermark [PDF -> JPG -> PDF]

Question

I am working with over thousands PDF files for a Sheet Music publisher.

All of these PDF files needs a preview PDF. A watermark for PDF files can easily be removed so I am asking for a true way to watermark our PDF:s in a batch operation.

PDF->Apply Watermark->JPG->Back to PDF

How can I do this? Is there a good tool for this operations?

Answer 1

The free route

ImageMagick can do the complete process for you, especially with the composite command's -watermark operator.

#!/bin/sh

# ImageMagick will pick the correct conversion formats based on filename suffixes, or maybe actual binary content?
InputPDF=$1
WatermarkImg=$2
OutputPDF=$3

pdfToImage=pdfToImage.png
imageWithWatermark=imageWithWatermark.png

# Convert PDF to image
convert           \
   -density 300   \
   -trim          \
    "$InputPDF"   \
   -quality 100   \
   -flatten       \
   -sharpen 0x1.0 \
   $pdfToImage

# Add watermark to intermediate image
composite          \
   -dissolve 15    \
   -tile           \
   "$WatermarkImg" \
   $pdfToImage     \
   $imageWithWatermark

# Convert intermediate image back to PDF
convert                \
   $imageWithWatermark \
   "$OutputPDF"

# Clean up
rm $pdfToImage $imageWithWatermark

I find the PDF to image conversion acceptable in terms of quality, though you can see some differences when looking at the before and after side-by-side, especially in how bolded glyphs seem less bold:

You can check this good post and its answers for a number of options for converting a PDF to an image, Convert PDF to image with high resolution.

I checked out PDFtoPPM, which was also highly mentioned in that thread, and I still see some degrading of the bolded fonts when converted:

Some more tiling Magick

I used this copyright symbol from Wikimedia Commons and this ImageMagick script:

#!/bin/sh

Infile="Copyright.png"
Outfile="Copyright_tiled.png"

h2=$(convert $Infile -format "%[fx:round(h/2)]" info:)

convert $Infile                   \
    \( -clone 0 -roll +0+"$h2" \) \
    +append                       \
    -write mpr:sometile           \
    +delete                       \
    -size 1224X1584               \
    tile:mpr:sometile             \
$Outfile

to create this staggered tiling (1224X1584 is the page size (8.5in x 11in) multiplied by 72 px/in, times 2 for a good density of tiles):