Add Page Numbers only accepts two format values, a plain number and a page-of-total format, and rejects anything else.
Microsoft's own support article for Word has users check Include Page Count in the page number gallery to produce a Page X of Y style label. Add page number X of Y to your Word document
Add Page NumbersAdd Page X of Y to PDF
The page-of-total format builds the label from the current page number and the number given to the last page.
Select the page-of-total format from the available options.
Upload the file to begin the page-numbering process.
Choosing the Page-Of-Total Format
Choose the page-of-total option to label each page with its number and the last page's number.
Review the format selection before processing the document.
Confirming the Total Page Count
Open the downloaded PDF and check the label on the final page.
Compare the displayed total number with the start number plus the page count minus one.
Count the pages manually if the printed total looks incorrect.
Continue with Custom Start Number or Font Size Limitations.
Frequently Asked Questions about Add Page X of Y to PDF
How do I select the page-of-total format?
Select the page-of-total option from the format menu.
Where do I upload the PDF file?
Upload the file on the tool's upload step to begin.
How do I verify the total page count?
Scroll to the last page and compare the printed total against the number printed for that page.
What format options are available?
Check the format dropdown for the plain-number choice and the page-of-total choice before submitting.