LibreOffice Writer is slow with my whole book open

Check the file format first

Writer's own format is ODF Text (.odt). A book kept as a .docx is converted every time it is opened and again every time it is saved, and on a long manuscript that conversion is where much of the waiting goes. If nobody needs the Word file until the book goes out, use File → Save As, choose ODF Text Document, and draft in that. Save a Word copy when an editor asks for one.

Settings worth changing

• Automatic spell checking. Toggle it off from the Tools menu or with Shift+F7, and check the whole book when you choose to.
• Word completion. Tools → AutoCorrect → AutoCorrect Options, then the Word Completion tab: clear Enable word completion. It collects words from everything you have open.
• AutoRecovery. Under Tools → Options → Load/Save → General (LibreOffice → Preferences on a Mac), a longer interval for saving AutoRecovery information means fewer pauses. Save by hand more often to make up for it.
• Rendering. Tools → Options → LibreOffice → View holds the graphics settings, such as hardware acceleration. What is offered varies by version and operating system; changing one and restarting is a fair experiment.
• Tracked changes. Edit → Track Changes → Manage lists every recorded change, with Accept All at the foot. Keep a marked-up copy before you press it.

Slow pastes, and splitting the book

Pasting a chapter from a web page or another word processor brings its styles along, and a book can end up carrying hundreds of them. Use Edit → Paste Special → Paste Unformatted Text (Ctrl+Alt+Shift+V, with ⌘ for Ctrl on a Mac) and apply your own paragraph style afterwards. It is quicker now, and it keeps the file lean later.

If the whole book is still sluggish, Writer has a built-in way to divide it. File → New → Master Document creates a file that gathers separate chapter documents, which you add from the Navigator (F5), and you then write in the small files and open the master to read through or print. Try it on copies before trusting a finished book to it.

In Tabularia

Here the manuscript stays whole and the page does the dividing: layout covers what is on screen, which Tabularia's benchmark measured from ten thousand words to a million. The Outline lists and moves between chapters the way the Navigator does, and chapters are structure rather than separate files to keep in step.

One thing to know before moving: Tabularia does not import .odt. Save the book from Writer in Word format (.docx) and import that. From a DOCX, Heading 1 becomes a chapter, and the footnotes Writer saved into the file come in as footnotes, endnotes included. Tables and images stay behind, and the import names what it left out. Exports do not include ODT either, though DOCX opens in Writer.