It's possible to add plain text word lists to Crossword Compiler lists using the Word List Manager. If you are converting a plain text word list, it must have the same format as the theme lists, i.e., one word per line like this:
First
Second
Third
Punctuation, capitalization and word order are not important. To add the list open the Word List Manager and select the word list to which you want to add it. Then select Add theme list/text file... from the Word List menu, and select the file that you want to add. You will then be prompted for which scores you want to give the added words.