fopen, fread, fwrite vs. XML Parser

[ChetUbetcha]

I have a Word template that I saved as XML. I used fopen, fread and then did a preg_replace on certain text. The echo of the information shows the updates, but when you go to open the XML document in word, it breaks and I get XML errors if I replace one word with multiple words.

My current version of PHP to Word works great, but it exports HTML tables and such. I want to use XML to get the proper headers and Table of Contents. How do I take my HTML elements that I'm currently using in my Word export, such as tables, and get them to replace the placeholder in proper XML format? Do I have to redesign those pages so they export as XML and then place them in the placeholders?

Any help would be greatly appreciated - this is my first day working with XML.

[ChetUbetcha]

From Word, I did the following:
Insert, Field, IncludeText and pasted the path of one of my php output files with the record id and everything worked perfectly. I did a test preg_replace on the id number and changed it to something else, but I get an error when opening the XML file in Word.

"A text/xml declaration may occur only at the very beginning of input."

My searches have all brought up comments on "white space" for certain headers, but I don't have that issue. My line of code is referenced in the middle of a bunch of junk that looks like this:

JKHSAD897213KJ4HIWUAFYD89876234RGBCE78TBAS877812

Any ideas?