headless Visio to PDF conversion fails with no output

Using LibreOffice on a CentOS server, I am running this command to try to convert Visio files:

/soffice --backtrace --headless --nologo --convert-to pdf *.vsd

So far no luck getting any output. Tracing with --backtrace gives

[Thread debugging using libthread_db enabled]
[New Thread 0x7fffe9a59700 (LWP 21023)]
[New Thread 0x7fffe1fb6700 (LWP 21024)]
[New Thread 0x7fffe15b5700 (LWP 21025)]
[Thread 0x7fffe1fb6700 (LWP 21024) exited]
[New Thread 0x7fffe1fb6700 (LWP 21026)]
[Thread 0x7fffe1fb6700 (LWP 21026) exited]
[New Thread 0x7fffe1fb6700 (LWP 21027)]
[Thread 0x7fffe1fb6700 (LWP 21027) exited]
[Thread 0x7fffe15b5700 (LWP 21025) exited]
[Thread 0x7fffe9a59700 (LWP 21023) exited]

Program exited normally.
No stack.

Am I missing something obvious? And, what could be the causes for the failure?