It is by no means clear from your post whether you're looking for:
• a single string with your known start and end keywords;
• multiple strings with the same start and end keywords; or
• singular/multiple strings with different start and end keywords,
in the documents. The code for each is quite different and, with the latter two, the question of where Word would look for the keywords comes into the equation.

Some clarification would be useful.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]