The Sparrow add-on is used to insert and refresh data inside Google Documents. This includes Google Slides, Google Sheets, and Google Docs.
If you open a non-Google document inside a Google Editor (e.g a PPTX file in Google Slides, or an XLSX spreadsheet in Sheets), you will still be able to open the Sparrow add-on and view all your data, but you will not be able to insert new data from the Sparrow add-on.
This is a limitation set in place by the Google add-on team, and is not something we're able to support at this time through Sparrow.
If you want to be able to add data to a non-Google document, we recommend converting the document to a Google Document (Slides, Sheets, Docs) and then re-open the Sparrow add-on.