We would like to change our uniquely developed website to a WordPress CMS with migrating the data.
Have you post this question in Wordpress Forum before you came here and post this question? The reason why I ask because it's their product/plaform so someone over in that forum can help you more on this issue.
Here's a link that you can read and learn more about migrate a website to WordPress:
I've developed an app that takes the data in a text file and moves it to specific columns in an Excel file. My computer has the Excel 2010 installed. So the application works fine with no issues. However we've begun to upgrade computers and software in the office ...