I’ve been using NetDrive3 version 3.17.960 to connect my Synology NAS via WebDAV.
After updating to version 3.18.1125, I’m having problems with PDF files from NAS. When I try to open them with Adobe Acrobat, I get the error message: “An error occurred while opening this document. Access denied.” (Translated from original German)
I was only able to resolve the issue by disabling “Run in AppContainer” in Acrobat (Edit > Preferences > Security (Advanced): Disable “Run in AppContainer”).
After switching back to version 3.17.960, the issue disappeared, which is why I suspect a bug in NetDrive.
Thank you for letting us know, and for the detailed description of the steps you took—this is very helpful.
What is happening
NetDrive 3.18 introduced a new driver based on WinFsp (Windows File System Proxy).
When Adobe Acrobat/Reader is set to “Run in AppContainer”, the PDF‑rendering process runs in a Windows sandbox that allows access only to certain “trusted” drive types. Unfortunately, WinFsp‑based drives are not on that list, so Acrobat’s sandbox blocks the file and shows the “Access denied” message. The same file opens normally when:
“Run in AppContainer” is turned off, or
an earlier NetDrive version (3.17 and below) is used.
Current work‑around
Disable “Run in AppContainer” in AcrobatEdit > Preferences > Security (Enhanced) → uncheck Run in AppContainer — or —
Add your NetDrive letter (e.g., N:) to Acrobat’s Privileged Locations (same Preferences page).
Stay on NetDrive 3.17.960 until we release a fix.
Please use whichever option best fits your security policy.
Next steps
Our engineering team is already investigating ways to make the new WinFsp driver compatible with Acrobat’s AppContainer sandbox. We will publish an update or hot‑fix as soon as a reliable solution is confirmed, and we will keep you informed of our progress.
We apologize for the inconvenience and appreciate your patience.