Interviewers and job descriptions sometimes make a point of requiring experience with "large" documents, and I always wonder what the underlying concern really is. What, in the mind of the interviewer or person writing the job description, distinguishes "large" documents from "small" ones?
Generating documents of any size requires skill with a word processor, including knowledge of how well the software handles documents that are primarily text as opposed to ones containing numerous graphics. As documents increase in size, however, navigation aids, organization and typographical style become more important.
Large documents inevitably need such items as tables of contents, indexes, cross-references and section breaks and associated headers, footers and pagination. These items can be tricky to use and maintain. Once the need for them is established, however, whether the document is 50 pages or 500 does not matter. The questions here, rather, are whether the technical writer both can determine when these conventions are needed and can implement them.