Task delayedTask = Task.Delay(TimeSpan.FromMinutes(5));
Task workerTask = Task.Factory.StartNew(() =>
{
     Aspose.Words.Document doc = new Aspose.Words.Document(inputFileName);
     doc.Save(Path.ChangeExtension(inputFileName,".pdf"));
});
 
if (await Task.WhenAny(delayedTask,workerTask) == delayedTask)
{
   // We got here because the delay task finished before the workertask.
}
else
{
   // We got here because the worker task finished before the delay.
}

您可以使用Microsoft.Bcl.Async向.NET 4.0添加async-await功能

编辑：

当您使用VS2010时,您可以使用Task.Factory.ContinueWheAny：

Task.Factory.ContinueWhenAny(new[] { delayedTask,workerTask },task =>
{
    if (task == delayedTask)
    {
        // We got here if the delay task finished before the workertask.
    }
    else
    {
        // We got here if the worker task finished before the delay.
    }
});

编辑2：

由于Task.Delay在.NET 4.0中不可用,您可以使用扩展方法自己创建它：

public static class TaskExtensions
{
    public static Task Delay(this Task task,TimeSpan timeSpan)
    {
        var tcs = new TaskCompletionSource<bool>();
        System.Timers.Timer timer = new System.Timers.Timer();
        timer.Elapsed += (obj,args) =>
        {
            tcs.TrySetResult(true);
        };
        timer.Interval = timeSpan.Milliseconds;
        timer.AutoReset = false;
        timer.Start();
        return tcs.Task;
    } 
}