I am developing an agent with Langgraph and I would like to use a specific pdf file as a base for my agent. However, when I am defining my code as a tool I am getting an error.
I am first reading the pdf file as a string which is then passed into the tool definition.

file_path = ("./myfile.pdf")
    
loader = PyPDFLoader(file_path)
pages = loader.load_and_split()
val = ""
for i in range(len(pages)):
    val = val +str(pages[i])

global file 
file = val.strip().replace("\n", " ")

@tool
def exponentiate(file:str)->str:
    "Read pdf"   
    return file

Error:

TypeError: ‘list’ object is not callable

What do I make incorrect here?