Do you have a PDF that was too large after merging using convert / ImageMagick?
Use gs or ghostscript as below, specify the output file and also the input file.
In the example below the output file is "outputfile-resized.pdf" and the input file is "original-pdf.pdf". Change the input file to the name of your pdf
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/prepress -dNOPAUSE -dQUIET -dBATCH -sOutputFile=outputfile........
If you can print other PDFs but not a particular one it is very likely that the PDF size is A4 (the longer, skinnier Asian paper size) instead of the North American letter size ( 8.5" x 11"). This breaks printing in most cases. Or it may print if you find a program that ignores the size issue.
Here is an example of an A4 being rejected by a printer in Ubuntu Linux via CUPS
Cannot print PDF CUPS Samsung C460:
Processin........