例如：
我PDF folder有PDF files：a.pdf，，，b.pdf等等c.pdf......
我使用类似的“PDF 阅读器”应用程序okular。
$ okular a.pdf
$ # read to the end of a.pdf and close okular window
$ okular b.pdf
$ # read to the end of b.pdf and close okular window
$ okular c.pdf
$ # read to the end of c.pdf and close okular window
$ # okular ...
或者像这样：
$ okular a.pdf b.pdf
$ # read to the end of a.pdf and switch to b.pdf, then close okular window of a.pdf
$ okular c.pdf
$ # read to the end of b.pdf and switch to c.pdf, then close okular window of b.pdf
$ okular ...
$ # read to the end of c.pdf and switch to ... , then close okular window of c.pdf
$ # okular ...