You probably do not need a special document camera. A decent compact camera should be sufficient for readable archive copies, and even many smartphones can work well.

For focus, use macro mode when shooting close-up documents. Compact cameras typically focus accurately at short distances, especially in macro mode.

For distortion, the camera matters less than setup. Keep the document flat, hold the camera parallel to the page, and use good, even lighting. A firm board or stable surface helps a lot. If you need straighter results, choose a camera reviewed as having low lens distortion, or correct perspective/distortion afterward in software.

If convenience matters most, a smartphone with a document-scanning or note app can simplify the workflow.

So yes, a portable solution exists—but it is usually just a normal compact camera or smartphone used with the right technique, not a specialized camera.