some question for RdkitGridFeaturizer.featurize input

## ❓ Questions & Help

I would like to use RdkitGridFeaturizer to characterise protein-small molecule complexes,

But I have some questions about the inputs to RdkitGridFeaturizer.featurize

Can I use the file paths of protein and ligand as inputs?

```
for example:
import deepchem as dc
featurizer = dc.feat.RdkitGridFeaturizer()
lig = 'ligand.sdf'
pro = 'protein.pdb'
featurizer.featurize([(lig, pro)])
```
```
output:
Failed to featurize datapoint 0.
```
What should I do?
Any help offered is appreciated!