Should my novel be one file or one file per chapter?

What each choice costs

A single file keeps the book whole. Find and Replace reaches every chapter, a renamed character changes everywhere in one pass, the word count is the book's, and exporting means saving one document. What it costs is weight. A 100,000-word Word file with comments, tracked changes, and a few images can grow slow to open and slow to scroll, and a single damaged file takes the whole draft with it rather than one chapter.

A file per chapter is light and quick, and it makes moving a chapter a matter of renaming files. The cost moves to the edges of the work. A search across the book becomes a search across a folder, a name change has to be made in thirty places, and at the end someone has to stitch the files together in the right order. Number the file names with leading zeros (01 Arrival, 02 The Letter) so the folder sorts in reading order.

Neither is wrong. Most writers who draft in a word processor do better with one file and a firm backup habit, because the tasks a single file makes easy are the ones done most often in revision.

Why not Word's Master Documents

Word has a feature built for exactly this question. In Outline view, a Master Document holds links to subdocuments, one per chapter, and opens them as though they were one file. It is rarely recommended. Word experts, including the long-running Word MVP community, have warned for years that master documents can become corrupted, lose track of their subdocuments, or damage the chapters they link to, and the advice most often given is simply not to use them. If you already have one, keep a backup of every subdocument before you touch the master.

There is a safer way to combine separate chapter files when the time comes. Open a new document, then on the Insert tab choose the arrow beside Object and pick Text from File. Insert the chapters one at a time, in order. That copies their text in rather than linking to it, and each inserted chapter takes on the formatting of the new document.

In Tabularia

The question does not come up, because a Project holds one continuous Manuscript with the chapters inside it. Search, find and replace, and the whole-book count all treat it as one work. When one chapter is all you want in front of you, the Working Scope shrinks what you see to that chapter alone. You get the calm of a separate file, and nothing is split. Reordering is a drag in the Outline, and the prose moves with the row.

Weight is handled differently too. There is no single file to damage: your writing is saved as you type, and Snapshots and History keep earlier states you can go back to. If your chapters are already separate Markdown or plain-text files, select them together when you import. Each file becomes a chapter, ordered by file name, and numbers sort as numbers, so chapter 2 lands before chapter 10. Word files import one at a time, so combine them first with Text from File and bring in the result.

What it will not do is keep chapters as separate files on your disk. If you rely on a folder of files for your own tools or version control, export to Markdown or DOCX when you need them.