I have installed all extensions which are shown here: Open File or Folder – KNIME Hub.
But I cannot found the component “Open File Or Folder”.
What is wrong?
That’s a Component, you need to download it from the Hub.
The extensions are prerequisites, some of the nodes used by the Component are part of those extensions.
Thank you. But I how do it download from the Hub?
You can either Drag and Drop it into KNIME or download it like any file:
After opening it with KNIME, you need to save the Component somewhere in your KNIME Explorer in order to use it.
Thank you 
Now if I know, it’s very easy.