tabula-java -d not converting several files to csv

[SeungKyoJin]

Hi I am using tabula-java in python like os.system(" ".join(["java -jar", jar, "-b ", nFolder, " -n -p all"]))

nFolder is directory.

I have 36 pdf files, which are looking alike, on it. 31 files are converted to csv succesfully but others not (make 0 byte csv)

How can I make sure every files will be converted successfully? If other information is needed please let me know.