Thank you for your responses. I appreciate your interest and help.
I have 7 artboards (A3 Landscape) in this particular document, a Company Profile, and this is the sequence the artboards are appearing when exported in pdf and then opened in Preview...1, 2, 4, 5, 7, 6, 3
I do realize the pages can be reorganized in Preview by dragging the thumbnails into the correct order, but unfortunately this doesn't permanently change the order in the original stored pdf file, so if I email the pdf file to a client for proofing, it is left up to client to re-arrange the order, which of course in not a desirable outcome.
Then of course, once completed, the file will have to be sent off to the printer in pdf format for printing and it will obviously need to have all of the pages in the correct order at this time.
Not sure where I go from here and would appreciate knowing if anyone else has had this same problem. This is the first job I have done with the program and also the first problem I have encountered. Up to now, I have been delighted with it and found it meets all of my needs.