Assigning an ICC profile
Pictures in the JPEG and TIFF formats can contain an ICC profile. An ICC profile is a description of how to interpret the colors in a picture. Different output devices (like a screen, or a printer) store colors in different ways, typical for the given device. Storing an ICC profile enables all devices that you work with to show your picture in exactly the same way, as long as they support color management and they are correctly calibrated. If a picture has no ICC profile, you can assign one to it, using Edit | Other | Assign ICC Profile… By assigning profiles to pictures, you ensure that pictures taken in a color space other than sRGB will be interpreted correctly. After you choose a profile, you can set how the operation will treat pictures that already have an ICC profile. If the Overwrite existing profiles option is checked, then old profiles will be overwritten by new ones. Adding a profile does not transform the colors inside the picture data itself.
This function depends on color management being active in the Color Management section of the program preferences.
Convert to Profile
This function converts picture data to the color space of the selected profile using the method selected under Reproduction. The Perceptual method is offered at first, and is Zoner's recommendation. When you perform this edit in the Editor and then save the picture, the changes are irreversible.
In the Browser, meanwhile, this is like all other edits always irreversible: the change is saved to file immediately!
So here as always: edit copies of your pictures, not the originals.
This function depends on color management being active in the Color Management section of the program preferences.