Comment by lo_zamoyski

They're likely viewing the electronic documents by analogy to photocopies with blacked out sections where there is nothing to distinguish the text from the redacting marks and nothing you can project out. They don't know the structure of the file format and how information in it is encoded or rendered, or even that there is a distinction between encoding and rendering.

(A better analogy might be the original physical document with redaction marks. If the text is printed using a laser printer or a type writer, and the marker used for redaction uses some other kind of ink - let's say one that doesn't dissolve the text's ink or toner in any way - then you can in principle distinguish between the two and thus recover visibility of the text.)