[itex]dW=\vec F \cdot d\vec r [/itex] is an infinitesimal amount work done over the infinitesimal displacement [itex]d\vec r [/itex],
where [itex] \vec F [/itex] is approximately constant during that displacement.
When this is evaluated over a path, then [itex]\vec F[/itex] and [itex]d\vec r [/itex] will vary as you progress along the path.
It's probably not a good idea to think of these [itex]d[/itex]'s as differentials (as in [itex]dW[/itex] is a differential of [itex]W[/itex]
since there is generally no such [itex]W[/itex] because the work done generally depends on the path. In thermodynamics books, this is sometimes written as [itex]đW [/itex].)