This is the best method for PDFs, documents, and spreadsheets.
You can use Safari to access the desktop version of Google Drive, though the interface is slightly more cramped on an iPad screen. download from google drive to ipad
Because iPadOS utilizes a file system that is more closed than a traditional computer, downloading from Google Drive works differently than it does on a Windows PC or Mac. The method you choose depends on what you want to do with the file. This is the best method for PDFs, documents,