Conversion code should not send unfiltered file names to the shell
I noticed the conversion code in src/main/java/nikita/webapp/service/impl/DocumentObjectService.java is building a command string to send to the shell for execution. This can be risky with unusual file names. It is better to build a argument list as a list and send it to the operating system for execution. I found an example in https://alvinalexander.com/java/java-exec-processbuilder-process-1 that might do this. At least it is using an argument list instead of a command string.