Problem adding new info to an old PDF File

I have an old book I wrote and saved in PDF years ago, like 15 years ago.

I tried to add some new info to the book so I can have it on my news blog

I have been able to get the old pdf to display, but when I try to add the book into my Word 2010 to put on my blog the final new file, it won't load the old file.

Any ideas on why new Word won't import an old pdf to merge into a new file?