Hidden Text - a better understanding of cause

We have run across a few scenarios in which we find text that is flagged as hidden text. But the text appears to be identical to the text on the page.  And the question I'm being asked to answer is: what is causing this scenario?  These files are the end-result of collaboration between two firms, so every step taken to create/modify the document is unknown to me. But I can define the following:

We have a PDF that was generated from MS Word (always), and sometimes has an added PDF page from another source.  When we sanitize the document, our team searches for Hidden Information.  Sometimes the results shows Hidden text. 

When we review the Hidden Text, it ends up being identical to the actual text on the page in the PDF. I have one example that I will use:

• Remove Hidden Information finds 1 page of Hidden text.
• When you click on SHOW PREVIEW, it shows the EXACT text of a page we have in the PDF. (every character = identical).
• When I click on SHOW VISIBLE, it doesn't preview anything (blank page) - which is odd because we have an actual page of text that can be seen and is identical to the 'Hidden text"
• When we inspect the page in the PDF, there doesn't appear to be any of the hidden text on that page
  • I may not know how to properly search/find this hidden text - but my investigation doesn't show anything obvious
• The Hidden text is exactly the same as the actual page in the PDF
• Just one page - out of dozens of pages built from Word and saved as a PDF - is showing as having HIDDEN TEXT
  • What would cause one page to have 'hidden' text triggered?
  • Did someone do something to this page? 

I attempted to research the cause of this, and I have read that text may be out of Order, and this may trigger a 'hidden text' prompt. But that leaves me a bit confused, and I'm hoping someone here might be able to clarify what is happening.

1. If the original document is in Word, and the PDF was built from this Word document, why would only one page show as Hidden Text?
2. What does Hidden Text mean, if it shows the same exact text as what is visible? (I.E., the text is obviously not hidden)
3. And why would this text NOT show as Visible via the Hidden Text menu when the text is very visible?

Our goal is to prevent this from happening in the future - if possible.  But I'm unclear on what may be causing this Hidden Text results.

Sorry - document is legal and confidential. I can't share for review.