What is PBM?
PBM is Netpbm's bilevel format - one bit per pixel, pure black or pure white, nothing in between. It is used for scanned documents, fax-era imagery and dithered art, and its packing convention surprises people: a 1 bit means black.
What is TIFF?
TIFF is the archival and print format - lossless, high bit depth, and flexible enough to hold multiple pages in one file. Scanners, publishing workflows and document archives lean on it heavily. Browsers have never displayed it, which is why it is offered here as a target rather than a source.