This case study uses a reading comprehension test and interviews to investigate how readers with and readers without reading or writing difficulties understand and perceive a decision on building permission in two versions: an original version and a version revised in accordance with the recommendations in a guide to plain language, Klarspråk­stestet för beslut. The aim is to contribute to usage guidance on adjusting texts for people with reading and writing difficulties and to study how comprehension and perception differ between those who have reading and writing difficulties and a control group. The study includes twelve participants, half of them with reading and writing difficulties. The theoretical framework of the study is plain language based on adequate simplifications and explanations for the intended recipient.   The result shows that there were differences between the groups’ mean scores on comprehension questions when they have read the decision in the original form, but there were no longer any differences between the groups when they had read the version in plain language. Just two people answered all the questions on the reading comprehension test correctly. One of the reasons for this may be that decisions on building permission are a type of decision that can be difficult to understand. Revising such decisions in accordance with the recommendations of the Swedish Language Council can facilitate reading comprehension, but does not automatically mean that the content is correctly understood or that the decision is perceived as being sufficiently adapted to the reader’s perspective. The result of the reading perception test shows that most participants were more positively disposed towards the plain language version of the decision. Another result is that there is a tendency for the last text the informants read to be perceived as better. All the informants’ responses to the questions on perception show that they want to find answers to their questions early in the text. The participants with reading and writing difficulties think that the technical terms should be explained in detail, while the informants without reading and writing difficulties think that these words are sufficiently well explained. The viewpoints expressed about the content show that the informants have different reading goals.