ConverSplitter Plus! only works with plain-text (i.e., .txt) files for time being. There are a number of practical reasons for this, but the main one is that adding support for other file types takes time.
There are a lot of options out there to automatically convert other file types (e.g., .docx, .pdf) to .txt, each of them with varying degrees of usefulness and difficulty. One program that I can recommend is Calibre, a fantastic and free e-book reader. This software can be used to convert between filetypes, and should be able to convert most files (including MS Word files) into plain text format. You can also “bulk convert” your files to do this for tons of documents all in one pass.
For more information, check out the manual:
On the other hand, if your texts are in a spreadsheet, you might find EZPZTXT will help accomplish this with ease. Depending on the format of your spreadsheets, you might not even need to use ConverSplitter Plus! at all!