Can one PDF have the main report numbered 1 to 10 and the appendices numbered separately from 1 again?

Why two passes

Each run of the tool applies one format and one start number to the range you give it. Two different sequences mean two different sets of settings, so you run it twice. What makes this safe is that pages outside the range get nothing added at all, so the second pass never goes near the pages you numbered in the first.

Pass one: the report

1. Open PDF page numbering and choose the 15-page report.
2. Pick Page {n} of {total}, type 1-10 in the pages field and leave the start number at 1.
3. Press Add numbers. Page 10 reads 'Page 10 of 10', because the total is the last number printed in this pass, which is right for the report on its own.
4. Download the file. Its name ends in numbered.

Pass two: the appendices

1. Choose the file you just downloaded, not the original, so both passes end up in one file.
2. Pick Custom template… and type Appendix {n}, or Appendix {n} of {total} if you want the total.
3. Type 11-15 in the pages field and leave the start number at 1. The summary line will say 5 of 15 pages will be numbered and that the first label, on page 11, is 'Appendix 1'.
4. Press Add numbers and download. Page 15 reads 'Appendix 5', and the total in this pass is 5.

Ideas that make the split clearer

• Use a different position for the appendices, say bottom right instead of bottom centre, or a different colour, so readers see at a glance they have moved into another section.
• If your contents page labels appendices with letters, A and B, note that the tool only fills in numbers. In that case number each appendix separately with a fixed template like Appendix A, p. {n}, one pass per appendix.
• The second pass produces a file name with numbered in it twice, so rename it before sending.

When splitting beats double numbering

If the appendices are sometimes sent on their own, it may suit you better to split them into a separate file with Split PDF and number each file independently. If the document is read and printed as one unit, the two passes above give the layout formal reports usually have.