If you do know the file name, enter it in the read file edit field.

You can then press Alt+F to hear the name.

Press tab to get to the read mode field.

Enter W, S, L or G if you want to change it, then press Alt+F to here what it is.
Press Alt+R or press Enter to read the file, press Alt+C to cancel.
If you select read mode W, the whole file is loaded into memory and spoken 
in the background. You can carry on with other activities. But, the file size
is limited to 64,000 bytes. Suitable for plain text and some control codes are
tolerated.

If you select read mode S, the file can be any size, and it can include some
control characters. No other activities can be performed during the reading.

If you select read mode L, the file can be any size, but it should be a plain
text file.  No other activities can be performed during the reading. This 
mode is suitable for unusual files with no sentences, or extremely long
sentences.

If you select read mode G, a special text file that you must create is read.
This file has a first line that says "Reader Group File" beginning at the
left margin. Each line after that can contain the path and file name of
a text file.  Reader will begin by reading the first file then pause until 
you press the space bar key, then read the next file, etc.  This is designed
for presentations where you may want to have Reader read passages 
between segments of your presentation. If you want Reader to read a
number of files sequentially, you can do it this way instead of typing the file
name each time.  After the last file is read, press the space bar again
to activate Reader's main window. See the file "sample.grp" to see how
this file is structured.  You can use any name or extension.