Which is the third step in filing, and is done by marking the index identifier on the papers to be filed?

The third step in the filing process is coding, which involves marking the index identifier on the documents that need to be filed. Coding is essential because it assigns a specific identifier to each document, facilitating easy retrieval and organization within the filing system. This step helps to ensure that each document is correctly categorized and can be found quickly when needed.

In a filing system, before coding, documents are typically sorted based on categories or other criteria, which organizes the files effectively. After the coding step, the next phase usually involves inspecting the documents to ensure there are no errors or missing items. Thus, coding serves as a critical transition point where documents are matched with their corresponding identifiers, leading to better management and accessibility of records.