You probably didn't find it because it isn't the 'base' form of the word. The base form is 'simple', and 'simpler' is the comparative form of this word : 'mais simples' em português.

Simpler means - easier, or less complex, less complicated, here are some examples of it being used. I think we had a simpler life in the olden days. Why is it simpler to use the other method of learning English? Choose the simpler way of doing it. http://www.theguardian.com/politics/2014/jul/16/most-people-developed-world-happy-ipsos-mori-poll http://www.sfgate.com/travel/article/Camper-vans-simpler-and-sleeker-than-RVs-gain-5629605.php http://www.theaustralian.com.au/sport/opinion/make-the-afl-penalty-system-simpler/story-e6frg7uo-1226994202103?nk=86559e803d311a0b4709f8aeb59abcf3

A simpler is a collector of medicinal herbs. It is best that you use more simple, or easier e.g. "This book is easier/more simple to read than that one.