Steps to reproduce:
1. Enable "Protected Mode at startup" in Adobe Acrobat Reader.
2. Completely exit Reader.
3. Open File Explorer and navigate to an SSHFS-Win/WinFsp network drive mapped as Z:.
4. Double-click a PDF. It opens normally.
5. Leave Reader running.
6. Return to File Explorer and double-click a different PDF on the same Z: drive.

Environment:
- Windows 11
- Adobe Acrobat Reader Continuous Release 2026.002.21931, 64-bit
- SSHFS-Win / WinFsp
- Network drive mapped as Z:
- Windows reports the remote path as \sshfs\kalmer@192.168.1.173....

Expected result:
The second PDF opens in the already running Reader instance.

Observed result:
Nothing happens. No error message is displayed.

Additional testing:
- The first PDF opens normally when Reader is not running.
- The second PDF can be opened with Reader's File > Open.
- The same PDF opens normally from Z: in Microsoft Edge.
- JPG files on the same Z: drive open normally by double-clicking.
- A PDF copied to a local drive opens normally.
- Disabling "Protected Mode at startup" completely resolves the problem.
- Re-enabling Protected Mode immediately reproduces it.
- Adding Z:\ as a Privileged Location does not resolve it.
- The Protected Mode log does not appear to contain the requested PDF path when the second open attempt fails.

This appears to be specifically an interaction between Protected Mode and passing a second document from Windows to an already running Reader instance when the document is on an SSHFS-Win/WinFsp filesystem.

A similar historical Adobe issue was reported with DFS/UNC network paths, and Adobe bug 3844582 concerned UNC/symbolic-link paths.