We have found one software suitable in our database for this conversion.
Microsoft Publisher is the only program that can reliably produce .pub documents from MS Word sources (.doc, .docx).
If you do not have access to this program, your only option for docx to pub conversion would be to rely on some 3rd party solutions, such as the online file conversion website ZAMZAR.
A desktop publishing application included in Microsoft Office and Microsoft 365 subscription plans
DOCX
Files with docx extension are documents written and saved using Microsoft Word word processor edition 2007 or later. DOCX format replaced the previously used DOC format, moving from binary files to Open XML schema-based documents. They are supported in almost every modern word-processing tools.
PUB
Files with pub extension are in most cases documents created in Microsoft Publisher, a desktop publishing application from Microsoft Office suite. PUB documents are much more complex than common Word files and give more emphasis to design and page layout, rather than actual text.