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Aspose.Words and Aspose.Slides support the feature to convert DOC/DOCX/PPT/PPTX files to PDF and PDF/A compliant format and I am afraid they do not support the feature to directly save the output in PDF/X-3 format. Besides this, we have an API named Aspose.Pdf for Java which provides the feature to create as well as manipulate existing PDF files. However, I am afraid currently it does not support the feature to convert PDF files to PDF/X-3 format. For the sake of implementation, we have logged this requirement as PDFNEWJAVA-34369 in our issue tracking system.
So once this feature is implemented, you can convert your Word/PowerPoint files to PDF format and then try using Aspose.Pdf for Java to render the output as PDF/X-3. Please be patient and spare us little time. We are sorry for this inconvenience.