Applying criterias to file submiting

Inputing file via the button works, but I want it to make sure the criterias for the file submiting are respected, How do I apply them so that the file meet the criterias and the error message is shown ?

Here's my code :

<form action="#"  class="form-horizontal">
    Upload File.
    <input type="file" id="fileinput" name="fileinp" class="form-control" multiple> 
    <br>
    <p id="ptagmsg"></p>
    <input type="submit" name="bxt" id="submitbutton" class="btn-primary" value="send">
</form>

document.addEventListener('DOMContentLoaded', function(){
                                           
    let inpFile = document.querySelector('#fileinput');
    var pTagMsg = document.querySelector('#ptagmsg');
    let kB = 1024;
    let mB = 1024 * 1024;
    let submitButton = document.querySelector('#submitbutton');
    submitButton.addEventListener('click', function(){                        
        var objFileList = inpFile.files;
        var fileObj = inpFile.files[0];
        let fileValue = inpFile.value;
        var fileName = fileObj.name;
        var fileSize = Math.round(fileObj.size / kB); // to kB OR mB
        var fileExt = fileObj.name.slice(-4);

        if(objFileList.length !== 0){
            // file is selected from file explorer.
            if(fileValue.length != 0){
                // check size and extenstion, file must be .pdf and greater than 200 kb.
                if((fileExt != '.pdf') || (fileSize <= 200) ){
                    pTagMsg.innerHTML = ' fileErrorMsg: file size must be 200KB and extension of .pdf';
                    pTagMsg.style.backgroundColor = 'red';
                    event.preventDefault();       
                } else {
                    // if file criteria is satisfied. 
                    pTagMsg.style.backgroundColor = 'green';
                    pTagMsg.innerHTML = ' File OK';
                    event.preventDefault();
                }
            }
        } else if(objFileList.length === 0){
            pTagMsg.innerHTML = 'please select a file.';
            event.preventDefault();
        }
                                                  
    });                             
});