Placed InDesign documents rasterize vector artwork when exported to PDF (regression vs. InDesign 202

I am experiencing an issue where vector artwork (.ai) becomes rasterized when placing an InDesign document into another InDesign document and exporting to PDF.

Workflow:

• An InDesign document contains vector artwork (native vectors and linked AI files with PDF compatibility enabled).

• This InDesign document is placed into another InDesign document using File → Place.

• The final document is exported to PDF (PDF/X-4, no transparency flattening intended).

Expected behavior:

All vector artwork should remain vector in the exported PDF. When opening the PDF in Illustrator, the artwork should be editable as vectors.

Actual behavior:

The placed content is rasterized:

• In InDesign, the placed document already appears pixelated even with Display Performance set to High Quality.

• After exporting to PDF, opening the file in Illustrator shows the placed artwork as a raster image, not vector data.

• This indicates the rasterization happens before or during placement/export, not just at display level.

Important notes:

• The linked InDesign file is available and shows no link warnings in the Links panel.

• The same source files and workflow produced correct vector PDFs in InDesign 2025.

• The issue appears to be a regression in newer versions, possibly related to placed INDD handling or transparency processing.

Why this is a problem:

This breaks modular workflows where InDesign documents are reused and placed into master layouts. Vector quality is lost, and the PDF output is no longer suitable for professional print production.

Attached files:

• Two PDF files are attached for direct comparison:
• one containing a placed InDesign 2025 document and exported from InDesign 2025
• one containing a placed InDesign 2026 document and exported from InDesign 2026

These PDFs allow direct side-by-side comparison of preview and output behavior.