When I first open Excel get three alerts:

Microsoft Excel cannot access the file '/Users/David/Desktop/.DS_Store'. There are several possible reasons:

• The file name or path does not exist.

• The file is being used by another program.

• The workbook you are trying to save has the same name as a currently open workbook.

                                                                                                OK

Alert

.txt…..dotx: file format is not valid.

Akert

The file format and extension of 'Your Recent Purchase Earned You a 10 Reward.pdf' don't match. The file could be corrupted or unsafe. Unless you trust its source, don't open it. Do you want to open it anyway?

                                                                        Yes              No