Hi
I feel you want to run a program within Excel and then get a file / excel document for each customer IE independant.
MAIL MERGE Will never do thi sby its very difinition and also mail merges are not so good if there are many differen letters / documnets to produce, sounds like you have variables ie customer A will be differed products from customer B, Word will fall flat on its face on this one unless you really VAB her heavy heavy.
Excel however could be made to do this from a few cood VBA scripts linking your array table to the leter document, this will be in each document so no wat each customer see others details, Un Like word which is 100 letters one folled by the next and so on. this would give 100 docunents in Excel.
Advantages does as you want and also you can find them, mail merges are dreadful to find a letter if you have 500 a day and save the word doc for 3 years you have to find the doc then teh letter from ??? I dont know.
If you name the Exel doc uniquley then you can search for say Jack and all my docs pop up and look for teh date and BINGO!!
Anne Troy has gone for Mail Merge and Jack says stay in Excel self contain it. Anne offers good ideas and as such i would chase these and then decide what way to go, as im a bit mix from the above post whats best
Just showing the difference between Excel documents and mail merge both have their place
Jack