[itsme]

I would leave the PDFs as they are and create separate songs per instrument, e.g. "America the Beautiful (trombone-3)",  "America the Beautiful (trombone-2)", and so on. Put them in collections per instrument / voice like "trombone-3", "trombone-2" and so on and creat setlists per event. MobileSheets can create these songs either by using snippets, copy the song and modify the page range or by using CSV import, the result is identical.

If you really want to split the PDF into separate files outside of MobileSheets, with PdfSaM Basic https://pdfsam.org/download-pdfsam-basic/ or PDF24 https://www.pdf24.org you can achieve that for free.