If you have mostly contacts, coils, MATH IBoxes and stages, those can come across with some minimal text editing (octal vs. decimal ID, MATHBCD vs. MATH) using the text-based import/export facilities in Designer and DirectSOFT. Just about everything else you must re-write, and more likely need to "Do-more-ify" it, e.g. how communication mastering instructions work is different (e.g. no "busy" bit), there is no accumulator or accumulator stack, BCD not natively supported (just a few conversion instructions), etc.
If it's a lot of simple stuff, try export Project from DirectSOFT and try to Import in Designer. You WILL get a bunch of errors, but the text editing should be minimal. However, if you have a bunch of "other" instructions, you are best off just re-writing it.
Here's an article on someone who "Do-more-ified" his 260 project. It was some effort, but it ended up cleaning up a LOT of code.
http://library.automationdirect.com/switching-to-do-more-saves-time-issue-27-2013/