in apex page i simply added one button and inputfile. 
I am doing in this way

  public PageReference SendRequest(){    
         
        binaryPdfString=String.ValueOf(inputFile);
        String key='XXXXXXXXXXXXXXXXXXXXX';
        String secret='xxxxxxxxxxxxxxxxxxxxxxxxxx';
        String formattedDateString= Datetime.now().formatGMT('EEE,   dd MMM yyyy HH:mm:ss z');
        String bucketname = '<bucketname>';
        String method = 'PUT';
        String filename = fname;
        HttpRequest req = new HttpRequest();
        req.setMethod(method);
        
        req.setHeader('Host','<bucketname>.s3.amazonaws.com');
        req.setEndpoint('https://<bucketname>.s3.amazonaws.com' + '/'+ bucketname + '/' + filename);
        req.setHeader('Content-Length', string.valueOf(binaryPdfString.length()));
        req.setHeader('Content-Encoding', 'UTF-8');
    //  req.setHeader('Content-Disposition', 'attachment'); 
        req.setHeader('Content-type', 'application/json');        
        req.setHeader('Connection','keep-alive');
        req.setHeader('Date', formattedDateString);
        req.setHeader('ACL','public-read');
        req.setBody(binaryPdfString);     
                  
        String stringToSign =
PUT\n\n'+'application/json\n'+formattedDateString+'\n/'+bucketname+'/'+bucketname+'/'+filename;
        String encodedStringToSign = EncodingUtil.urlEncode(stringToSign,'UTF-8');        
        String signed = createSignature(stringToSign,secret);
        String authHeader = 'AWS' + ' ' + key + ':' + signed;
        req.setHeader('Authorization',authHeader);
        String decoded = EncodingUtil.urlDecode(encodedStringToSign , 'UTF-8');        
       
        Http http = new Http();
        try {
             HTTPResponse res = http.send(req);          
             System.debug('*Resp:'+String.ValueOF(res.getBody()));                    
             System.debug('RESPONSE STRING: ' + res.toString());
             System.debug('RESPONSE STATUS: '+res.getStatus());
             System.debug('STATUS_CODE: '+res.getStatusCode());
             if(res.getStatusCode()==200 && res.getStatus()=='OK')
             {
                 success= filename +' File has uploaded Successfully.';
//this is executing 
                  inputFile=null;
             }

            } catch(System.CalloutException e) {
            system.debug('AWS Service Callout Exception: ' + e.getMessage());
        }

    return ApexPages.Currentpage();
}

 

    public string createSignature(string canonicalBuffer,String secret){
        string sig;
        Blob mac = Crypto.generateMac('HMACSHA1', blob.valueof(canonicalBuffer),blob.valueof(secret));
        sig = EncodingUtil.base64Encode(mac);  
        return sig;
    }