If you have rows of fixed-width data (in this case the first 12 characters of each row) and you want to put a tab at the end, put this in your “Find what” box in Microsoft Word:
(^13*{12})
and put this in the “Replace With” box:
\1^t
and check the Use Wildcards option
The “^13″ is a newline character (^p doesn’t work when using wildcards)
