When creating a PDF document from a Word document, different PDF generators create different files. Some difference is due to the way different fonts are handled. You can for example read more on kerning here: https://en.wikipedia.org/wiki/Kerning.
Here is an example of a Word-document generated into a PDF in different ways all displayed on the screen in Windows 10 using Adobe Reader DC with 300% zoom. The limited screen resolution makes it hard to see the finer details.
Microsoft Word 2016. Created with Microsoft Print to PDF virtual printer. Good quality with no visible kerning problems in this example. However the generated text is a bit dark.
Microsoft Word 2013. Created with save as.. and the as a file type PDF. Take notice of the kerning problems marked with yellow.
Microsoft Word 2016. Created with PDF X-Change virtual printer. Take notice of the kerning problems marked with yellow.
Microsoft Word 2016. Created Adobe Acrobat Pro XI virtual printer Adobe PDF.
Microsoft Word 2016. Created with PDFCreator virtual printer.
Microsoft Word 2016. Created with Save as.. and then as the file type PDF with the higher quality.