Converting Microsoft Word to PDF

I wrote a manuscript for my book in Microsoft Word.  I then paid a huge sum for someone to convert it to PDF.  This person made many errors in doing this.  However, finally I had it in PDF which was made into a book.  Now I need to have more books printed but I need to fix a few typo errors.  The printing company said all I needed to do is send in correct pages in PDF format and simply slip them in to replace the old page.  My first problem is when I looked at the finished book and typed the pages over again correctly in Word it did not fit the page the same way.  Even thought I used the same page set up.  ( Need to be able to just slip the new page in place of the old one to the printer.) I am looking at trying to buy a software for converting or having someone convert it again for me but why won't it just come out looking exactly like the finished book.  Please someone out there help me. I can't go back to the person who originally converted for me.