Programs with .docx, .wpd, .rtf, .xls, .xlsx, .pdf, or .txt format?

I am trying to upload a doent for a college application and my essay is on microsoft word. for some reason it won't upload. it says it supports .docx, .wpd, .rtf, .xls, .xlsx, .pdf, or .txt format, but i don't know what program I should use to be one of those. please help me.