Gets or sets whether a synchronous read of a remote document that needs bytes not yet fetched blocks on the request. When off, the read throws PdfRangeNotLoadedException, and a page is read after awaiting its PrefetchAsync(CancellationToken). On by default, except on the browser platform (and WASI), which cannot block on HTTP; turning it on there has no effect.
public bool SynchronousRangeFetch { get; set; }
Spec #33, viewer capability 5 (the asynchronous prefetch boundary).