procedure setReadOnly(value : Boolean);

The function setReadOnly() forces the library to open files in read-only mode. It is useful if you do not want to modify your file accidenatly.
The function isReadOnly() allows you to get current mode.
You have to call setReadOnly before openning a file.

function isReadOnly: Boolean;

var
    dbf: TcdbfapiPlus;
begin
    dbf := TcdbfapiPlus.Create;
    dbf.setReadOnly(True);
    if (dbf.openDBFFile('c:\tmp\example.dbf')) then
    begin
        // your code
        dbf.closeDBFFile;
    end;
    dbf := nil;
end;