I would like to know whether DOpus pro(version 12) possesses a tool that allows to create stickies destined to a single file. It should open as a warning, recommendation or alike when hovering over the file name or applying a single click (left or right) to it.
Labels and status icons allow you to visually highlight files in various ways.
File descriptions allow you to attach a text note to any file (for some file types, it requires NTFS so may not work with NAS devices or things like FTP sites, inside of archives, and so on). The Description and User Description columns can show the notes in the file display, or can be placed inside the info-tips that appear when you hover over the files. ("Description" shows some additional information about files, such as image type and dimensions. "User Description" shows just the notes you typed yourself.)
The options under Preferences / File Operations / Copy Attributes can be important if you use either of these. Preserve the descriptions of copied files will copy descriptions.
Copy metadata (comments, keywords, etc) copies labels, assuming labels are stored in the filesystem (Preferences / Favorites and Recent / Labels / Automatically store labels in the file system if possible). If labels are not stored in the filesystem, they will point to particular file paths rather than the files themselves, so any file renamed to that path will inherit the label. That is useful in some situations, and the other way is useful in others.
Also note that if you edit files using other programs, some of them may cause labels and/or descriptions to be cleared, depending on whether they preserve the metadata of the files they edit or replace with new versions.