It's possible if the application that is used to open that type of file has scripting/macro support such that we can control it from a document macro in Docman. Let's say it's a Word document, then it would be possible. Probably it's possible for some other applications as well. For sure in AutoCAD (DWG file format). If it's a PDF, and if you can find some PDF tool that can draw a red cross (or whatever) like that, it can probably also be called by the Docman macro before the file is opened (also by a macro).