The View tab of the Import and Paste Special dialog lets you see the contents of the imported or pasted file, divided into columns. This can be especially helpful if you are importing from a comma- or tab-delimited text file. A quick look can let you know if your columns are formatted correctly.
Once you've pasted linked data into a Prism data table, click Open File to open and edit the data file. If it is an Excel file, you'll open Excel. If it is a text file, you will open a text editor.