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Navigating the reader

Updated on August 5, 2026

Theca's reader gives you full control over how you move through a book: jump to the chapter you need, adjust the zoom, and move page by page without losing your place.

Table of contents

If the book has an index, the table of contents button appears on the left side of the toolbar. Clicking it opens a side panel listing all the chapters and sections of the book. Click any entry to jump directly to that point.

In EPUB files, the table of contents is built from the file's own structure. In PDF files, Theca uses the embedded index if one exists; otherwise the button does not appear.

If you open a book from a search result, the reader jumps automatically to the page and passage that matches your query.

Moving between pages

  • Previous page and Next page in the toolbar move one page backward or forward.
  • The counter in the center shows the current page and total (for example, 12 / 340). Click the number to type a page number directly and press Enter to jump to it.

Zoom

The Zoom out (-) and Zoom in (+) buttons in the toolbar control the zoom level:

  • In PDF files, they adjust the scale of the document (the percentage is shown in the toolbar).
  • In EPUB and TXT files, they increase or decrease the font size rather than scaling the page.

Scroll mode and dual page

  • Scroll mode — for PDF and EPUB, you can switch between page-by-page navigation and continuous scrolling. The button in the toolbar shows the active mode.
  • Dual page — shows two pages side by side, useful on large screens. Available for PDF and for EPUB when scroll mode is off.

Loading states for a large PDF

When you open a PDF, Theca shows a placeholder while the document loads. If the file is large, the message "Large book — this may take a moment" appears below a progress bar. If loading takes too long, the reader shows the notice "This book is taking too long to open" with a Retry button.

Resource unavailable

If you reach the reader through a link that points to a book that no longer exists in your library, Theca shows the notice "Resource unavailable" explaining that the referenced book or resource may have been deleted, along with a Back button to return to the library.

Frequently asked questions

Can I go to a specific page without using the arrows? Yes. Click the page number in the center counter, type the page you want, and press Enter or click outside the field.

Does dual page work in EPUB? Yes, as long as scroll mode is not active. If scroll mode is on, dual page is not available.

Why don't I see the table of contents button in my PDF? The button only appears if the PDF has an embedded index. If your PDF does not have one, the button is not shown. You can generate one from the book detail panel.

Is the zoom level saved between sessions? The reader applies the zoom you set during the session, but it does not persist after you close the app.

Next step

Navigating Theca's reader — NoxDragon Docs · NoxDragon