THotPDF.UseObjectStreams Property

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

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

Works naturally alongside 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 that even minimal PDF parsers can still locate the document roots and decrypt the content.

Setting UseObjectStreams to true silently falls back to false when UseXRefStream is off (type-2 entries cannot be represented in the textual xref table, per the 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, whilst 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 typically amounts to 20-40% of the post-FlateDecode file size. A 30-page graphics-only smoke test goes down from 14502 bytes to 8488 bytes (-41.5%).