THotPDF.UseObjectStreams Property

Pack eligible indirect objects into PDF 1.5 /Type /ObjStm container streams (ISO 32000-1 7.5.7) to cut on-disk PDF size.

When UseObjectStreams is true (and UseXRefStream is also true), EndDoc packs every eligible indirect object - dictionaries, arrays, numbers, names, strings, booleans, nulls - into one or more /Type /ObjStm container streams per ISO 32000-1 7.5.7. The cross-reference stream then references the packed objects through type-2 entries (host ObjStm object number + entry index inside that stream), so individual N G obj ... endobj framing bytes and per-row textual xref entries are eliminated.

Pairs naturally with the UseXRefStream property for the most compact PDF 1.5+ writer pipeline. The ObjStm packer leaves stream objects, the encryption dictionary, and the trailer-pointed Catalog and Info dictionaries uncompressed so even minimal PDF parsers can still locate document roots and decrypt content.

Setting UseObjectStreams to true silently downgrades to false when UseXRefStream is off (type-2 entries are not representable in the textual xref table per spec) or when Version is below PDF 1.5.

It is also forced off under PDF/A-1: ISO 19005-1 (PDF 1.4, clause 6.1.4) forbids compressed object streams together with the cross-reference streams they ride on, so EndDoc emits a classic xref table whenever PDFACompliance names a part-1 level, while PDF/A-2 and PDF/A-3 (PDF 1.7) leave it available

Code Example

HPDF := THotPDF.Create( nil );
try
  HPDF.FileName := 'c:\Output.pdf';
  HPDF.Version := pdf15;          // Object streams require PDF 1.5+
  HPDF.UseXRefStream := true;     // ObjStm references need a /Type /XRef stream
  HPDF.UseObjectStreams := true;  // Pack indirect objects into /Type /ObjStm
  HPDF.Compression := cmFlateDecode;
  HPDF.BeginDoc;
  HPDF.CurrentPage.TextOut( 100, 100, 0, 'Compact PDF 1.5 output' );
  HPDF.EndDoc;
finally
  HPDF.Free;
end;

On documents dominated by small indirect dictionaries (multi-page documents, annotations, AcroForm widgets, structure-tree elements, Optional Content layers) the saving is typically 20-40% of the post-FlateDecode file size. A 30-page graphics-only smoke test shrinks from 14502 bytes to 8488 bytes (-41.5%).