I remember when Office 2007 came out there was a dispute with Adobe about supporting PDF files in Office. At the time Microsoft had to provide this support with an add-on to Office 2007. That add-on is no longer available from Microsoft. However, you can still download it from third party sites. For example,
2007 Microsoft Office Add-in: Save as PDF or XPS
Filename: SaveAsPDFandXPS.exe
Filesize: 933 KB (956,344 bytes)
Note that for programs like Word 2007 it could only Save as a PDF but not open this file. You had to keep the original .docx file for future editing.
Here is a screenshot of Word 2007 showing the ability to save as a PDF file.
View attachment 1648