The phrase "multiple files" refers to more than one file or document. It means having several different files instead of just one.
Sentences with «multiple files»
In order to convert various files simultaneously, it provides batch handling which makes the conversion of multiple files at the same time easier. (ebookconverter.com)
In addition to electronic books, the current Reader models support multiple file formats for personal documents and music. (sonyinsider.com)
You can also attach multiple files in 1 email. (fkbt.com)