A family of Microsoft word processing software products for creating web, email, and print documents.
If you use Word to open any PDF file, it will always convert the contents into Word's internal format, because Word cannot directly edit the PDF format.
To open a PDF file without conversion, you must use a PDF program instead. There are many, from the (expensive) Adobe Acrobat Professional to the many free PDF readers you can download from the Internet. Some of the latter have paid versions that can let you edit the content.