Product & Version
Acrobat Reader DC (64-bit)
Affected: 2025.001.20630
Tested: 2025.001.20756

OS
Windows 64-bit

Summary
Acrobat Reader becomes unresponsive when opening multiple PDFs using the /n command-line argument (separate processes). Issue reproducible outside any third-party apps.

Steps to Reproduce

Open Command Prompt
Run:

"C:\Program Files\Adobe\Acrobat Reader DC\Reader\AcroRd32.exe" /n "C:\Path\File1.pdf"

Run again with a different PDF
Scroll/switch between files

Expected
PDFs remain responsive

Actual
App becomes unresponsive

2025.001.20630: also logs AdobeCollabSync.exe failure
2025.001.20756: no failure, but still sluggish/unresponsive

Frequency
Consistent in 2025.001.20630

Notes

Reproducible via command line only
/n required to open files in separate processes (used for tracking)
Behavior has worked for years; not new

Impact
Degraded performance with multiple PDFs open