Is there any way to import fields from an Excel spreadsheet into an Adobe document, and have these imported fields become separate Sticky Notes that can be moved around and placed on the PDF?
In theory yes, but I don't see it being very practicable.
A comment requires a page number, position, author, date and time, and contents, so you'd have to define all those in the spreadsheet or dynamically calculate them within the script. You could write the XLS file to a text file (CSV) and use scripting to import it (a folder-level script can use the new util.readFileIntoStream and util.stringFromStream methods) but the comments would be locked to a particular page.
Europe, Middle East and Africa