I stole this, but this is the solution I used from Jeremiah Willcock and another answer website. Not digging through history at the moment. I lied, I did. (Tully @https://askubuntu.com/a/626301)
I needed a file small enough to email.
To combine images into a PDF
(from in working directory use command line:
user@box:/home/user/scans/:$
convert 1.png 2.png convertoutput.pdf
To shrink using ghostscript after combining
(I used on kde default system almost):
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/default \
-dNOPAUSE -dQUIET -dBATCH -dDetectDuplicateImages -dCompressFonts=true \
-r150 -sOutputFile=output.pdf convertoutput.pdf
My file had 14 images (19MB after convert, gs made it 1.6MB, quality was still great). The output file is called output.pdf.
