I am using `pdftk` library to extract the form fields from the pdf .Everything is just running fine except the one issue that i got a pdf file [pdf file link](http://www.uscis.gov/sites/default/files/files/form/i-9.pdf). which causes the error is given bellow

```
Error: Failed to open PDF file: 
   http://www.uscis.gov/sites/default/files/files/form/i-9.pdf
Done.  Input errors, so no output created.

```

command for this is 

```
root@ri8-MS-7788:/home/ri-8# pdftk http://192.168.1.43/form/i-9.pdf dump_data_fields

```

the same command is working for all other forms . 

**Attempt1**

I have tried to encrypt the pdf to unsafe version but it produce the same error . here is the command

```
pdftk http://192.168.1.43/forms/i-9.pdf input_pw foopass output /var/www/forms/un-i-9.pdf

```

**Update**

this is my full function to handle this 

```
public function Formanalysis($pdfname) 
    {
         $pdffile=Yii::app()->getBaseUrl(true).'/uploads/forms/'.$pdfname;
        exec("pdftk ".$pdffile." dump_data_fields 2>&1", $output,$retval);
        //got an error for some pdf if these are secure 
        if(strpos($output[0],'Error') !== false)
        {
            $unsafepdf=Yii::getPathOfAlias('webroot').'/uploads/forms/un-'.$pdfname;
            //echo "pdftk ".$pdffile." input_pw foopass output ".$unsafepdf;
            exec("pdftk ".$pdffile." input_pw foopass output ".$unsafepdf);
            exec("pdftk ".$unsafepdf." dump_data_fields 2>&1", $outputunsafe,$retval);
            return $outputunsafe ;
            //$response=array('0'=>'error','error'=>$output[0]);
            //return $response;

        }

        //if (strpos($output[0],'Error') !== false){ echo  "error to run" ; }   // this is the option to handle error 
        return $output;

    }

```