A forum search wouldn't have gone astray. See, for example:
[SOLVED] Large Scale Find Replace, Loop to all files in folder (vbaexpress.com)
http://www.vbaexpress.com/forum/show...l=1#post230215 (you might want to combine this with the replacement implementaion in http://www.vbaexpress.com/forum/show...l=1#post239647)
http://www.vbaexpress.com/forum/show...l=1#post400838
And, since you cross-posted this at MS Office forums, a search there would have turned up:
Created VBA to Find and Replace in Body, Header and Footer with Highlighting the replacement text (msofficeforums.com)
VBA code to run macro across all documents in folder (msofficeforums.com)
amongst others...