we can do:
arrFiles | String Array
arrFiles = Directory.GetFiles(MyDirPathVar,"*.*",SearchOption.AllDirectories)
arrFiles = Directory.GetFiles(MyDirPathVar,"myFileNamePlusExtension",SearchOption.AllDirectories)
For the existence check we use: arrFiles.Any()
Also have a look here:
[CheatSheet] - Filesystem APIs - News / Tutorials - UiPath Community Forum