# Core Concepts This page explains what pdf2image does to the page when it loads, and how that decides when you can call `convert()`. ## Dependencies Injected on Load pdf2image does not bundle pdf.js or JSZip. As soon as the script runs, it inserts these elements into ``: | Element | Target | Purpose | |---|---|---| | `` | `https://cdnjs.cloudflare.com` | Opens the connection early | | `` | pdf.js, pdf.worker.js, JSZip | Downloads early | | ` ``` ## The Global Class Both the UMD and ESM builds set `window.pdf2image`; the ESM build only adds `export const pdf2image = window.pdf2image` to export the same class. Each instance holds its own `file`, `type`, `scale`, `filename`, and conversion results, with no state shared across instances. ## Runtime Constraints | Constraint | Reason | |---|---| | Browser only | Depends on `document`, `canvas`, and `navigator` | | Needs network access | pdf.js, JSZip, CMaps, and the stylesheet all come from CDNs | | CSP must allow the CDNs | `script-src` needs `cdnjs.cloudflare.com`; `style-src` needs `cdn.jsdelivr.net` | ## Related Pages - [Conversion](/conversion) - [Architecture](/architecture)