Storing script execution output in a bash variable [duplicate]

I am running an executable file from inside a bash script. I need to store the output of this execution in a variable. The executable file is running and giving correct result when I just run the executable, but there is error when I try to store the output to a variable.

The executable file is a tool called pdfToolBox, and it runs like given below:

./<path_to pdfToolBox> --extracttext <path_to pdfFile>

As shown above, the executable takes a command and a file to check. The complete available documentation of this tool is found here https://help.callassoftware.com/m/pdftoolbox/l/657637-installation-and-activation-of-pdftoolbox-server-cli . I am using the CLI interface in my project.

Now, I am creating a script that accepts the executable path, and the pdf file path and executes the command mentioned above. So I can call it from the terminal like:

./check_file.sh <path_to_pdfToolBox> <path_to_pdfFile>

Here is the code I have written:

#!/bin/bash

# we will use this to find if there is any text in the file being checked
# return value from here will be used to load the proper profile for file check
find_text() {
    local containedText=""

    $containedText="./$pdfToolBox --extracttext $fileToCheck"

    echo "$containedText"

    # process containedText to check file
}

# argument 1 is the path of pdfToolBox executable
# argument 2 is the path of pdf file to be checked
pdfToolBox=$1
fileToCheck=$2

find_text

I expected the output to be saved in the variable $containedText, but I receive an error like this:

./findText2.sh: line 7: =./pdfToolbox --extracttext data/Test-Briefpapier-A3-sg.pdf: No such file or directory

I have tried using both relative paths and actual paths but none seem to work and return the same error. However, if I change line 7 to

./$pdfToolBox --extracttext $fileToCheck

instead of

$containedText="./$pdfToolBox --extracttext $fileToCheck"

it executes without any error. I cannot point out the problem here. Please help.