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

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.

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: http://zeroset.mnim.org/2015/01/07/flatten-pdfs-with-ghostscript/

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'