for me the invoice PDFs are not searchable. They are text, when i open them i can mark text in Acrobat.
But when i search in MacOS for a word which is in the PDF i normally find the PDF. Also in Apple Mail.
But i can not find PDFs which are generated with Invoice Ninja, unfortunately.
I also can search it in Adobe Professional and Reader on Mac.
But the Mac Finder can not find the PDFs. For the mac finder the PDFs are not searchable as it seems…
Also not in Mac Mail App (which uses the same search, i assume)
Could be an issue with Spotlight index on that particular Mac. I just tested it in Mac OS 12.6.8 - Preview found my search word when opening an invoice PDF using the Preview app, and when searching in the Finder it also found the file containing the word I searched for. Maybe try rebuilding your Spotlight index on that computer and try again. Also, check System Preferences in Spotlight - Privacy to make sure you don’t have the containing folder excluded from indexing.