on Jane Friedman site:

A writer’s investment in their book is more than time and creativity. Our words, and sometimes visuals, are then turned into electronic files—another investment. Publishers cover the cost of creating publishing files, while indie authors bear the expense of creating the files for their books.

This has long been the case, but when bringing a book to market in today’s shifting publishing landscape, doesn’t it pay to be proactive in terms of file ownership?

A traditionally published author may one day have their publishing rights reverted. For indie authors, the firm or freelancer you hired to prepare files may close or disagreements may develop. Or perhaps you want to publish your next book using a different team.

The costs to republish a book or to make changes to a book—or to take your book to a new designer—depend on whether or not you have the appropriate files. Common file types used in publishing are Microsoft Word, Adobe InDesign (an industry-standard software program for typesetting manuscripts), and PDF. The type of file you have determines how easy, and how costly, it will be to make changes to the book.

Here are five real-life author stories about corrections and republishing, and an explanation of why having the files—the right files—is important: