There is a difference between reading and reciting the Quran without tajweed and tajweed. If someone recites the Quran, he/she may not be observing specific rules that make their recitation sound better and more proper. On the other hand, if they want to recite the Quran with tajweed, they must learn specific rules to perfect their recitation that sounds like authentic Arabic.
Indeed, when someone recounts the Quran without tajweed, they are still observing some rules of tajweed such as the pronunciation of the letters and vowels, the madd (مَدّ) or lengthening of long vowels, and so on. However, tajweed is a more advanced version of reciting the Quran with many more rules that they must learn to beautify their recitation.