Hi Kay,
If your customers are sophisticated enough to deal with e-mailed invoices and other documents, they're probably sophisticated enough to re-size the window if it open in an unexpected size.
What happens if you open it in Adobe Reader (not Acrobat)? Many of your customers may only have V6.x and so may never notice. Perhaps we'll wait until one of your customers makes a comment - we have changed nothing at this end, and we think it is unlikely that we have any control over this setting in any case.
Thanks for all your careful sleuthing. Isn't Saturday a day of rest?
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Andrew Bates