Is there a way to flatten a .pdf image from the command line?

Question

In GIMP, I can import a PDF, and use the GUI to flatten it (if it was made with many layers) by selecting Flatten Image in the Image dropdown menu. I can then export the PDF with a new filename.

I would like to automate this. Is there some way to do it via the terminal?

Answer 1

I found these 2 method via Google, in this thread titled: Re: Flattening PDF Files at the UNIX Command Line.

Method #1 - using Imagemagick's convert:

$ convert -density 300 orig.pdf flattened.pdf 

NOTE: The quality is reported to be so so with this approach.

Method #2 - Using pdf2ps -> ps2pdf:

$ pdf2ps orig.pdf - | ps2pdf - flattened.pdf

NOTE: This method is reported to retain the image quality.

Answer 2

Ghostscript (gs) worked better than pdf2ps and convert for me. Quality was hardly degraded and file size is small.

gs -dSAFER -dBATCH -dNOPAUSE -dNOCACHE -sDEVICE=pdfwrite \
-sColorConversionStrategy=/LeaveColorUnchanged  \
-dAutoFilterColorImages=true \
-dAutoFilterGrayImages=true \
-dDownsampleMonoImages=true \
-dDownsampleGrayImages=true \
-dDownsampleColorImages=true \
-sOutputFile=document_flat.pdf document_original.pdf

Found here. Note the comment about removing the / before LeaveColorUnchanged.

Answer 3

ghostscript changed their default for flattening annotations in late 2016.

To simply flatten a PDF now, you need -dPreserveAnnots=false

So a simple command line is now

gs -dSAFER -dBATCH -dNOPAUSE -dNOCACHE -sDEVICE=pdfwrite \
-dPreserveAnnots=false \
-sOutputFile=document_flat.pdf document_original.pdf

Answer 4

Although convert will keep the same file size I've found it to be slow.

The pdf2ps ps2pdf method is faster but I noticed for me it was increasing the file size.

pdftk is nice because it is not only fast but also retains a similar file size.

This is what I use to bulk flatten a directory.

    function pdfflatten () {
        pdftk "$1" output "$2" flatten
    }
    export pdfflatten
    alias pdfflattenDIR='mkdir flattenedPDFs; for i in `seq $(ls *.pdf | wc -l)`; do a=`ls *.pdf | head -$i | tail -1`; pdfflatten "$a" flattenedPDFs/"$a"; done'

Answer 5

I frequently need to flatten PDFs or make them image-only. I wanted to do this quickly from within Nautilus instead of going to a terminal, so I created two Nautilus scripts based on the previous answers. I am sharing the instructions in case they are useful to others.

Create script to flatten PDFs:

1. Go to the Nautilus script folder ~/.local/share/nautilus/scripts/
2. Create a new shell script file (eg FlattenPDF.sh)
3. Make this file executable (eg Natiuls Properties → Permissions → Allow executing file as program)
4. Insert below text into the file:

#!/bin/bash

# Flattend PDFs    

IFS='
'
for file in $NAUTILUS_SCRIPT_SELECTED_FILE_PATHS
do
  if [ -f "$file" ]; then
    base=${file%.*}
    ext=${file##*.}
    newname=${base}_flat.pdf
    gs -dSAFER -dBATCH -dNOPAUSE -dNOCACHE -sDEVICE=pdfwrite -dPreserveAnnots=false -sOutputFile=$newname $file
  fi
done

Create script to create image-only (text not searchable or selectable) PDFs:

1. Go to the Nautilus script folder ~/.local/share/nautilus/scripts/
2. Create a new shell script file (eg ImageOnlyPDF.sh)
3. Make this file executable (eg Natiuls Properties → Permissions → Allow executing file as program)
4. Insert below text into the file:

#!/bin/bash

# Image-only PDFs    

IFS='
'
for file in $NAUTILUS_SCRIPT_SELECTED_FILE_PATHS
do
  if [ -f "$file" ]; then
    base=${file%.*}
    ext=${file##*.}
    newname=${base}_img.pdf
    gconvert -density 200 $file $newname
  fi
done

Restart nautilus (eg type nautilus -q to quit Nautilus and then open Nautilus from the Dash again). If you right-click on a file, you should see the Scripts menu with the new scripts.