PowerGREP is designed to search through text documents. It can search through spreadsheets by first converting the spreadsheet into a plain text document. This plain text conversion contains the text or numbers shown by all the cells. Cells are delimited with tabs, rows are delimited with line breaks, and sheets are delimited with page breaks. Content not shown by the cells, like formulas, are not included in the plain text conversion and are thus cannot be searched for with PowerGREP.
To be able to search through spreadsheets as if they were plain text documents, you need to set the "file formats to convert plain text with" on the File Selector panel to a configuration that converts spreadsheets to plain text. In the configuration, the option "Use PowerGREP's built-in decoder to convert files to plain text" should be turned on for the file formats "Microsoft Excel 95 to 2003 (DOC)", "Microsoft Excel 2007 to 2016", "Quattro Pro", and "Lotus 1-2-3 (WKS)". Default configurations that do this are "proprietary formats", "all formats", "attachments & proprietary formats", and "attachments & all formats".
With one of these configurations selected on the File Selector panel, you can use the Editor|Open menu item to open a spreadsheet and view it in PowerGREP's built-in editor. The text you see in the editor is the text that PowerGREP would search through when the file is included in an action. You won't be able to edit the file. You can edit its plain text representation if you first use File|Save As to save it as a plain text file.
If you want to search only through spreadsheets, add the file mask of the spreadsheet formats you want to search through to the "include files" box on the File Selector panel. For Excel, use *.xls;*.xls[xm]. For Quattro Pro, use *.wq;*.wb;*.qpw;*.wkq. For Lotus 1-2-3, use *.wk[s134].
This file selection is available in the PowerGREP5.pgl library as "Office: Search through spreadsheets".
To indicate which spreadsheets to search through, click on the folder that contains them in the "folders and files" tree. Then select Include File or Folder or Include Folder and Subfolders from the File Selector menu.
Finally, prepare and execute your search on the Action panel.