PdfViewer

A BitPdfSource is the document: FromUrl (fetched through the registered HttpClient), FromBytes, FromBase64 or FromStreamAsync. AllowDropFile also opens a pdf dropped onto the viewer.

Height and Width take any CSS length. Unset, the viewer fills its host's width and is at most 780px tall, shrinking with the viewport. A fit mode re-fits whenever the box resizes.

ToolbarItems (a flags enum) picks the built-in groups - a group left out takes its find, print or download shortcut with it - and ShowToolbar hides the bar. ToolbarStartTemplate and ToolbarEndTemplate add your own content, with the viewer as its context. OpenFile adds a file picker; handle OnFileOpened to take the picked file yourself, and MaxOpenFileSize caps what it reads.

Four side panels: page thumbnails, bookmarks (the document outline), embedded attachments and optional-content layers. DefaultSidebar picks the one open when a document loads. Thumbnails render lazily, and a panel with nothing to show keeps its toggle disabled.

InitialZoomMode picks the starting fit: Automatic (fit width, capped at 125%), FitWidth, FitPage, FitHeight or ActualSize. ZoomPresets replaces the dropdown's percentages; MinZoom, MaxZoom and ZoomStep bound and pace every zoom, including Ctrl+wheel and pinch, which keep the point under the cursor in place.

ScrollMode stacks pages vertically, lays them in a horizontal row, wraps them, or shows one at a time (a swipe turns it on touch). SpreadMode pairs them like an open book (Even keeps page 1 as a cover), and CursorTool switches dragging between selecting text and panning. Presentation mode (Ctrl+Alt+P) combines them fullscreen and restores the layout on exit.

Matches are counted over the whole document without rendering it, and painted with the CSS Custom Highlight API. The options match case, whole words and diacritics (off by default, so resume finds résumé), and paint every match or only the current one. Search, SetSearchOptions, FindNext and ClearSearch do the same from code.

RenderMode: Html (default) lays pages out as prerenderable positioned DOM; Canvas paints them onto a canvas - far fewer DOM nodes - while selection, find and links keep working. TextCoalescing: Compact merges same-line runs into one span per line, at a small position cost. BackgroundRendering moves the work off the UI thread where the runtime has a spare one.

The toolbar's info button opens the properties dialog. The same data is on the reference - Metadata, Permissions, PageLabels, FormFields, StructureTree and the parsed Document - for indexing or auditing without parsing twice.

An encrypted document asks for its password in a built-in dialog. WithPassword carries a known one on the source, OnPasswordRequested replaces the dialog with your own UI, and ShowPasswordPrompt=false reports the failure through OnError instead. RespectPermissions enforces the owner's no-print / no-copy flags (advisory, so off by default).

Select an encrypted pdf file to try it:

LoadingTemplate replaces the page-shaped placeholder while a document is fetched and parsed, EmptyTemplate the message of a viewer with no document, and ErrorTemplate that of a failed load, with the message OnError receives. A failure is announced as an alert either way.

Every state change is reported: loading, page, zoom, rotation and sidebar, each rendered page (OnPageRendered), load progress of a URL source (OnProgress), non-fatal parse diagnostics (OnWarnings) and failures (OnError). OnDownloading and OnPrinting run first, whatever started them (toolbar, shortcut or code): this one renames the download and can block printing.

Events:

CurrentPage, Zoom and Rotation are two-way bindable. Bound one way (no Changed callback) the value is the host's to control, and the reader's moves arrive through the events instead.

Every toolbar action is a method, so your own chrome can drive a viewer whose toolbar is hidden. Print takes the whole document, a page range, or (PrintCurrentPage) one page, at each page's true size. GoToDestination lands on the exact spot a bookmark points at, GetSelectedText reads what the reader highlighted, and OpenAsync, ExtractText and RenderPageHtml are API-only.

First

Prev

/

Next

Last

Zoom -

100%

Zoom +

Fit page

Rotate

Thumbnails

First bookmark

Selected text

Download

Print all

Print page

Print 1-2

Present

Every string the viewer shows or announces comes from Texts (a BitPdfViewerTexts); set only the ones you replace.

With focus inside the viewer the familiar shortcuts work (and override the browser's Ctrl+ F / P / S), and each toolbar button announces its own through aria-keyshortcuts; EnableKeyboardShortcuts=false hands them back. The thumbnails are a listbox and the bookmarks a tree, each one tab stop moved by the arrow keys. Each page is a named group whose text is read once, its links are named tab stops, and page moves are announced; the dialogs trap focus and close on Esc. A disabled viewer (Disabled) keeps showing the document with its chrome inert.

BitParams with a BitPdfViewerParams sets defaults - texts, toolbar, size, zoom, styles - for every viewer under it. A viewer's own value wins (the second keeps its own toolbar).

FromStreamFactory opens a fresh readable, seekable stream for each viewer load and owns it until replacement, closing or disposal. Password retries reuse that stream. Keep the source in a field; prerendering and interactive rendering each invoke the factory. The initial stream position is the PDF origin, and the remaining length must fit Int32. Keep its bytes and length stable; same-length changes cannot be detected. A caller needing different ownership can return a non-disposing wrapper.

Stream sources use a bounded raw-byte cache. Server parsing, page/thumbnail rendering, search and print work run off the circuit even when BackgroundRendering is false. Download streams the original bytes without retaining a complete server buffer. Decoded resources and cached decrypted stream buffers are outside the raw-byte cache budget. GetBytes() returns null. GetBytesAsync explicitly returns a complete caller-owned copy without retaining it. Use RenderPageHtmlAsync, ExtractPageTextAsync and ExtractTextAsync; their synchronous counterparts throw for an active stream source. The document model, XRef and raw-file streams are valid only during that load; released access throws ObjectDisposedException.

This example is for a file accessible to the server. FromUrl keeps its buffered behavior; HTTP Range loading is a later contribution. Browser uploads keep the FromStreamAsync snapshot path because IBrowserFile streams are not seekable and do not support synchronous reads. The viewer coordinates copies with rendering and asynchronous helpers. In a browser, await a copy before reading Document or its raw streams directly.

Style and Class reach the root; Styles and Classes reach each part. The public --bit-PdfViewer-* CSS variables restyle a viewer here, or every viewer from :root - the third one also reads in a dark mode through --bit-PdfViewer-page-filter.

Component's Style & Class:

Styles & Classes:

CSS variables:

With Dir set to Rtl the toolbar, sidebars and find box flip; the page navigation and the zoom out / zoom in pair keep their left-to-right order, as numbers do, and page content keeps the orientation the document defines.