The prefix is assigned based on where that PDF file is in the sort order. In other words, if a PDF file was the 15th file in your list of PDFs to be reviewed on your eCopy, then that PDF must have a "015_" prefix. Note that there is no correlation between the 3-digit prefix and the content or section location of a file. For example, if a mechanical testing report PDF was in Section 10 of the document, this does not mean that the prefix of "010_" must be applied.