Some files may be greyed out and unselectable when you try to import them. This means that they are not in one of the formats that Goodnotes supports.
To import a non-supported file, like Excel, convert it to PDF first and import that PDF into the app. Here's one way to do it:
- Open that file on your iPad. For example, if the file's in iCloud Drive, you can open it there.
- Tap the Share button > Print (or a similar function in the external app).
- Spread with 2 fingers over the Print Preview panel.
- Tap the Share button > Open in Goodnotes.