How to bulk update doc page size to make the page size consistent?

I have a bunch of doc files and all files paper size format is different. I want to convert all those doc file formats to A4 size using soffice command.

Is there any way so I can convert those files using the command line and create a bulk process?

There’s no command-line option to do that (LibreOffice command line interface is not meant to edit files); you might be able to do that e.g. creating some macro and then using the command line to open files and run the macro. Or by using PyUNO to control LibreOffice from scripts.