The straightforward passive werden + Partizip II is never wrong at an advanced level, but relying on it too heavily makes a text feel labored and unpolished, especially in academic writing, formal reports, and business correspondence. For this reason, written and elevated German has developed a set of stylistic alternatives to the passive (Passiversatzformen) that convey the same meaning — above all "can be done" or "must be done" — through phrasing that is more compact and elegant. Mastering these alternatives is one of the clearest signs of linguistic maturity in a German learner.
The first and most flexible alternative is sich lassen + Infinitiv, which always corresponds to passive + können: Das Problem lässt sich lösen literally means "the problem lets itself be solved," i.e. it can be solved. Second, sein + zu + Infinitiv can carry either of two meanings depending on context — possibility or necessity: Die Aufgabe ist zu lösen may mean it can be solved or it must be solved, and context alone decides which. Third, adjectival suffixes such as -bar and -lich turn a verb directly into an adjective expressing passive possibility: lösbar (solvable), essbar (edible), verständlich (comprehensible) — the shortest of these alternatives and the most common in scientific and technical writing. Fourth, man + an active verb is the simplest and most conversational solution, turning the sentence entirely from passive into active with an unspecified general subject. Finally, there is the so-called Rezipientenpassiv, formed with bekommen/kriegen + Partizip II, which foregrounds the recipient rather than the agent: Ich bekomme das Paket geschickt means "the package is being sent to me," and it only works with verbs that take an indirect object (Dativobjekt) in their active form.
The key difference among these alternatives is register and semantic precision: -bar and sich lassen are usually limited to the meaning of possibility alone, while sein + zu can also carry the sense of obligation, and man is the least formal of them all. There is often no single equivalent structure covering this whole range of nuance in a learner's own language, so the real challenge lies in training the ear to pick the alternative that fits the register, rather than translating literally.
A frequent mistake at the advanced level is applying -bar to verbs that don't morphologically accept it, or confusing sich lassen (which always requires the subject to be the very thing the action is done to, not a human agent) with sein + zu — producing the erroneous Er lässt sich einladen when the learner actually intends plain objective possibility: that sentence in fact means the person himself permits being invited, a meaning quite distinct from the neutral possibility the context called for.