Two PDF.co parameters that trip people up. `pages` is a 0-based, comma-separated list of indices or ranges: `'0,2-5,7-'` means page 1, pages 3-6, and page 8 through the end. Leave it empty to process all pages. Note the 0-based indexing: page 1 is `0`, not `1`, so `'1-3'` skips your first page. For password-protected PDFs, pass the document password in the `password` parameter; without it the call fails or returns garbage instead of a helpful error. If your source PDFs come from users, always pass `password` through and surface the auth failure cleanly rather than treating it as a corrupt file.

Context: Web source (PDF.co official samples repo, pdfdotco/pdf-co-api-samples on github.com): conversion calls take a `pages` parameter as a comma-separated list of 0-based page indices or ranges (example: '0,2-5,7-' for page 1, pages 3-6, and page 8 onward); leave it empty for all pages. Protected PDFs take a `password` parameter with the document password; leave it empty for unprotected documents.