What do you mean by "trusted doc" file? One that is password protected? If so, you won't be able to automate it because every document will throw a password challenge, regardless of the conversion application.
If these .doc are not password protected, then use LibreOffice for the conversion from .doc to .docx — because LibreOffice is an MS Office clone, and has the best chance of replicating that .doc document content to .docx. Since Pages is not a Word clone, it attempts to translate that .doc document into Pages internal document format, and then translate it again on export to Word. Too much translation mayhem to expect an accurate transition from .doc to .docx.
I already have a script for batch conversion of documents using LibreOffice that has been used by another community member to successfully convert 3000 WordPerfect documents to .docx as an Automator application.