State

usePdfState(selector) reads the viewer’s state (ViewerState) and re-renders its component only when the selected value changes. Outside React, viewer.store.subscribe(listener) hears each change and viewer.store.get() returns the state.

const page = usePdfState((state) => state.currentPage);

The store publishes when the document loads, the mounted pages or the current page change, or the view does; scrolling and zoom gestures change nothing in it per frame.

Field	Meaning
status, error	"idle", "loading", "password" (see Encrypted documents), "ready", or "error", and the error’s message.
passwordReason	"required" or "incorrect" while the document waits for a password, otherwise null.
progress	{ loaded, total } bytes of the document received, total null when the server did not say; null before any arrive.
pageCount, currentPage	Pages in the document, and the zero-based page being read: the one nearest the viewport’s center, except that the current page stays current while all of it is in view, and that navigation makes the page it shows current.
pageLabels	Each page’s label, such as "iv" or "A-3", when the PDF defines them; otherwise null.
scale, zoomMode	CSS pixels per PDF point; "fit-width" or "fit-page" while the page is fitted as the viewport resizes, otherwise "custom".
rotation, spread, scrollMode	The view’s clockwise rotation (0, 90, 180, or 270); "none", "odd", or "even"; and "vertical", "horizontal", "wrapped", or "page" (see Scroll modes).
tool	What a mouse drag does: "select" text, or scroll the document with the "hand".
search	The search in progress or done (see Search).
outline, canGoBack, canGoForward	The document outline (null while it loads), and whether back() and forward() have a position to return to.
permissions	What the document permits (see Permissions); null while it loads.
documentView	How the document asks to be shown (see The document’s initial view); null while it loads.
metadata	Title, author, subject, keywords, creator, producer, creation and modification dates, PDF version, and language; null while it loads.
attachments, layers	The document’s embedded files and its layers (see Layers and attachments); null while they load.
annotationTool, annotationState, annotationStyles	The annotation tool, undo, redo, and selection, and each tool’s style, with annotationEditing on (see Annotations); the last two null while it is off.
layout, first, last	The page boxes at the current zoom, and the mounted pages.
document	The engine’s open document; usePdfDocument() returns pdf.js’s proxy of it.