Looking for a movie where a man reads a forbidden book and a mongoose-like creature appears

Hi everyone, I'm trying to remember the name of an English-language movie I watched some years ago. I don't remember the full movie, just a particular part of it. In this part, a man finds a strange or forbidden book and goes to a library to read it. Despite warnings not to read it, he does. The book tells a story about a mysterious man from another world (or dimension) who came to Earth many years ago and harmed people. This man had a creature that looked like a mongoose (or something similar), which he kept as a kind of servant or familiar. After reading the book, the man leaves the library and starts seeing parts of the story come to life — especially the same mongoose-like creature and the evil man from the book. The strange man starts following him, just like in the book. There were no big monsters or ghosts — just that creepy, otherworldly man and his weird animal. I remember this being only a part of the movie, not the entire plot. Does anyone recognize this film? Thanks in advance!