These are international discussion communities and the term "word system" might mean something different depending on the individual, the application, and their locale. Stating MS Word would have been quite clear.
Since you want to avoid MS Word converting PDFs to .docx documents, you will want a means to view the PDF without Word touching it. Select the Apple File Manager and see the list of documents. Tap and hold on the PDF and a secondary menu will appear where you select Quick Look. That will allow you to view your PDF.
Alternatively, you could install the free Adobe Acrobat Reader from the iOS/iPadOS App Store. I did, but Quick Look may be all you need.