Excel files open differently depending on the recipient's software and screen - columns shift, fonts substitute, formulas may be hidden. A PDF locks the layout so everyone sees the same page.
Steps
Open the Excel to PDF tool and upload your .xlsx or .xls file
Click Convert - the server renders the spreadsheet via LibreOffice
Download the PDF
Getting a clean result
Set the print area in Excel first if only part of the sheet matters
Wide tables may split across pages - consider landscape orientation or shrinking columns
Charts and formatting are preserved; check the output once before sending
Going the other way
Need the data back as a spreadsheet? Use Excel to CSV to extract the values, or CSV to Excel to rebuild a .xlsx from comma-separated data.