If you do not want spaces on the file that was uploaded in your form, you can use a php script after the form is processed to rename the file. After many different attempts, this one worked for me.

//This code will rename the uploaded file replacing the spaces in the filename
//In RSForms Pro, put this code
//Manage Forms --> Form Properties --> PhP Scripts --> Script called after form has been processed

// Initialize Variables
$filename='';
$fromPath='';
$origFilename='';
$fromOrig='';
//* Get the filename
foreach ($_FILES as $name => $value) {
if (is_array($value)) {
$value = implode(', ', $value);
}
if ("name" == $name) {
$filename=$value;
}
}
// Stores Original Name, removes Spaces
$origFilename=$filename;
$filename=str_replace(' ','_',$filename);
// This will rename the original file
$fromOrig = JPATH_SITE.'/your/directory/for/uploads/'.$origFilename;
$fromPath = JPATH_SITE.'/your/directory/for/uploads/'.$filename;
rename($fromOrig, $fromPath);