Server-side document rendering
Definition
Converting a document into page images on the server, so the browser displays rendered pages rather than parsing the original file itself.
The alternative — client-side rendering — ships a parsing engine to the browser and hands it the file. That works acceptably for PDF and poorly for everything else, because writing a browser-based renderer for DOCX, XLSX, DWG and MSG is a decade of work nobody wants to fund twice.
Rendering server-side inverts the properties. Format coverage becomes a server-side library problem rather than a JavaScript bundle problem. The client stays thin regardless of how complex the document is. And the original bytes never reach the browser, which means viewing a document and possessing it stop being the same act.
The cost is real and worth stating: rendering consumes CPU and memory on your servers, and pages have to travel over the network as images. In practice the load is dominated by page complexity rather than document length, since pages are rendered on demand rather than all at once.
In Doconut
Every format goes through the same path. Viewer.OpenDocumentAsync() rasterizes pages server-side and returns an opaque token; the JavaScript widget then requests pages by token. The browser never receives the source document.
Related terms
Document viewer SDK
A library you embed in your own application so it can display documents, as distinct from a hosted service you upload documents to. The SDK runs inside your process; the service runs inside somebody else's.
Text layer
The machine-readable text stored inside a document alongside its visual appearance. It is what makes search and text selection possible, and it is exactly what a scanned page does not have.
Opaque session token
An identifier that carries no meaning to whoever holds it — it references server-side state rather than describing it, so a client cannot read it, modify it, or guess a neighbouring value.