压缩PDF

$ gs -sDEVICE=pdfwrite -dNOPAUSE -dBATCH -dPDFSETTINGS=/ebook -sOutputFile=output.pdf input.pdf

起作用的是PDFSETTINGS选项，产品质量由高到低可以取值为：/prepress，/printer，/ebook，/screen。

merging PostScript, pdf Files

If GostScript is installed, PostScript files merging can be done via the followed command:

$ gs -sDEVICE=pswrite -sOutputFile=output.ps -dNOPAUSE -dBATCH file1.ps file2.ps file3.ps

gs also has other similar usages, such as merging pdf files:

$ gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=output.pdf -dBATCH algebra.pdf biology.pdf

dPDFSETTINGS may be used to specify the quality: 

• dPDFSETTINGS=/ebook (low quality, 150 dpi images) 
• dPDFSETTINGS=/printer (high quality, 300 dpi images) 
• dPDFSETTINGS=/prepress (high quality, color preserving, 300 dpi imgs)
• dPDFSETTINGS=/default (almost identical to /screen)