Scalable and Random-Access PDF Loading

HotPDF keeps large loaded files responsive by delaying stream copies and compressed-object parsing until the data is required

File-backed stream windows

Unencrypted documents opened with LoadFromFile retain immutable stream bodies as source-file ranges

Reads seek to the required range and release the source handle immediately, so the original file remains replaceable on Windows

OpenLoadedStreamSourceSlice creates an independent read-only view over an unfiltered source range without copying or materialising the lazy stream

The first write materialises the stream in memory when it is at or below LoadedStreamMemoryThreshold, or in an owned temporary file when it is larger

Lazy object streams

Each decoded /Type /ObjStm container is indexed by authoritative xref object number without parsing every member during open

Catalog, page-tree, and later link resolution materialise individual members once and reuse their parsed objects

A full rewrite automatically materialises every remaining member, while an unchanged file-backed save can preserve the original bytes directly

ReleaseDecodedStreamsAfterSave releases an object-stream container only after every indexed member is materialised, and ReleaseLoadedDecodedStreamCaches exposes the same safe release pass on demand

Custom random access

Derive from THPDFRandomAccessSource and implement GetSize plus ReadAt to load from HTTP ranges, databases, archives, or virtual storage; override IsRangeAvailable when fetched ranges can arrive independently

LoadFromRandomAccessSource adapts the source to HotPDF's seekable parser and can optionally own the source for the document lifetime

Progressive linearized availability

GetProgressiveLinearizedLoadInfo reads only a bounded first-object probe, validates /L, /O, /E, /N, and /T, and reports the first-page prefix plus main-xref tail ranges required for early display

ReadProgressiveLinearizedFirstPageSection copies the available first-page section in 64 KiB chunks after both required ranges are present, while operation cancellation remains active between reads

THPDFProgressiveLoadStatus distinguishes an unavailable header, a non-linearized or invalid source, missing first-page ranges, first-page readiness, and complete-document readiness

Parallel image and high-ratio stream optimization

OptimizeLoadedStreams can select frmHighRatio to try four deterministic zlib strategies at maximum compression and retain the smallest standards-compatible Flate stream

OptimizeLoadedImagesParallel decodes eligible image streams into bounded adaptive storage, compresses up to the caller's worker limit, and commits results serially in source-object order only when the requested byte saving is achieved

Diagnostics

GetLoadedStreamCacheInfo reports source-backed, memory-materialised, and disk-materialised stream counts
GetLoadedObjectStreamCacheInfo reports indexed and materialised members, cache hits and misses, and retained decoded bytes
GetLoadedObjectLifecycleStatistics separates clean, dirty, released, and must-write objects