This topic comes up every 3-6 months. It's a different language each time, but I will give the same answer.

You will almost never like the results of doing a direct translation from language X to language Y, especially if they're as different from each other as a Pascal-type language vs. a scripting language. A small and incomplete list of the reasons why would include:

• LOCs between languages can vary up to 50x. My personal estimate for Pascal -> Perl would be about 20x - as in Perl is 20x more concise than the equivalent Pascal code.
• Many languages do not have the same concepts. (Q.v. Beating the Averages) This means that you will be ending up with Perl code that is highly inefficient. If you're converting because you convinced your boss there would be a performance benefit, s/he will be sorely disappointed.
• Verification of the translation is going to be a bitch. Especially on 500K lines of Pascal-type code.
• Database access in Perl is generally done through DBI. I'm betting 4D doesn't have a similar feature.

Basically, I'm saying that you will want to rewrite the application from the ground up, with all the risks that entails. It will be a smaller risk and a greater reward than translating 500K lines of Pascal-type code to Perl. Plus, this can be seen as a good opportunity to update the business rules, as needed. It will probably take between 2-5 man-years. Good luck! (You'll need it ...)