dmd error - unrecognized file extension

[Evan Burkey via Digitalmars-d-learn]

Hi there, I have a problem that is eluding me, hoping someone can 
help me see the light. I'm on Windows 10 using the latest version 
of dmd. I have a directory with 2 files: "version.txt" and 
"versioncheck.d". version.txt contains a single line of text. I 
have the line:

    immutable version = import("version.txt");
and my dmd switches are:

    dmd -J. .\versioncheck.d

but dmd fails with "Error: unrecognized file extension". I've 
searched the internet but found very little about this problem. 
Hopefully I'm just missing something simple.

Thanks!