clang-format -style=file fails

I’m trying to configure a custom style options file for clang-format v6.0.0 running on Windows 10 Pro 64-bit. I started out by generating a configuration file based upon the llvm style using the following command line, which worked fine:
clang-format -style=llvm -dump-config > .clang-format

The documentation for clang-format states the following:
“When the desired code formatting style is different from the available options, the style can be customized using the -style=”{key: value, …}" option or by putting your style configuration in the .clang-format or _clang-format file in your project’s directory and using clang-format -style=file."

So just as a test I used the unchanged .clang-format file I generated above and used the following command line:
clang-format -style=.clang-format Test.c
The result was a message that said “Invalid value for -style”. I then changed the name of .clang-format to _clang-format and tried it again but the result was the same. So, my question is, “How do I specify a specific style options file?”