Compared with Word documents, PDF files are more universally supported on all kinds of devices. If you choose to send Word documents to others, you may consider converting them to PDF files first. Both Word for desktop and mobile have the export utility that can help users convert Word to PDF.
If you have many Word documents on iPhone, the Word app is not a good options as there are too many steps involved. For bulk Word doc conversion, you should use a more professional PDF converter. This PDF converter is my go-to app for PDF conversions. It is so powerful that it can create PDF files from virtually any popular files and formats. It is easy to use, I can convert many file types directly from many other apps without even need to launch the PDF converter in advance.
Converting Word to PDF on iPhone
Find the Word document in Files or other file manager apps where the Doc, Docx files are saved on your iPhone or iPad. Select the word file, then tap the Action menu at the bottom left corner, choose Convert to PDF, the Word doc will be converted to PDF instantly.

You will see a prompt telling you the PDF is ready on your iPhone screen. Tap Go to File to view your PDF in the PDF converter or tap Done to stay in the current Files or other app where your Word document, then repeat the easy steps to convert more Word doc to PDF.

All the PDFs you create are saved in the Documents tab in PDF Converter.
Convert PDF to Word on iPhone iPad
Need to convert file formats the other way around? Please refer to these steps to convert PDF to Word doc on iPhone iPad.