According to "우리말 형태소 사전" (2012), the suffix, 본(本), means a book or books and a document and documents.
복사본 (a copy or copies) and 사본 are interchangeable unless 사본 refers to exactly copying the original version of a book, books, a document, or documents. Practically, 사본 and 복사본 refer to the same: It is okay to regard 사본 as a shortened form of 복사본. Now we write something not only by hand but also on computers, so 복사본 and 사본 can also be used to mean a copy or copies produced on computers.
복사 is what you or machines do to make 복사본. 복사 means not only copying or tracing the original version but also making a smaller/larger version of it. With the advent of computers, it is also used to stand for "copy" as in "Copy & Paste." Copy machines are called 복사기.
사본하다 and 복사하다 are the verbs of 사본 and 복사, respectively, but I believe that people rarely use 사본하다.