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

Answer 2

And here it is unwatermarked again
#ZachYoung I used some different image magic, also scriptable, the point is:-
Although "What's done cannot be undone" Macbeth (Act 5.1. 63-4) is very true especially within a PDF or image. We also know and expect that it too applies to any PDF (de)constructs. Thus depending on value of a forgery it will always be worth engineering a partially reversed copy, fit for scrutiny or use, but will like the watermarked copy, still not be the original, however all the same, may look almost just as good.
The Idiom implies don't bother yourself about it. Its best not done in the first place.
The nearest to best, is use a watermark exactly the same as the text outlines, like this:-