Cannot apply any filter

[1113]

Hi,
I imported segmentation file from itk-SNAP in vtk format in Paraview(ver 5.9.1).
Every filter looks in gray and is not applicable to my model

Also when I put the cursor on contour filter icon, ‘Requires an input’ message shows.

How can it be fixed? Specifically I want to apply contour filter to my model.
Is it the problem of my file?

Thank you in advance.

[mwestphal (Mathieu Westphal (Kitware))]

Press apply.

I've just opened my dataset. I can't add filters, and everything is greyed out

Make sure your dataset is selected in the Pipeline Browser Click apply (in the Properties tab) if the apply button is green

[1113]

Thanks so much