Understanding Apple’s compression — and how not to ruin it twice
HEIC uses advanced codecs to retain fine texture at efficient sizes. A careless converter re-encodes aggressively, then wraps a damaged bitmap in a PDF — you “preserve” nothing. HEIC to PDF without losing quality means: decode carefully, embed at full resolution, avoid gratuitous recompression, and let the PDF container carry the fidelity you already captured. Convert pictures to PDF should not mean “make them look like a social-media thumbnail.”