delete all but the first page

Usually, you would use an Action to do something like this in Adobe Acrobat Pro (Standard does not have the "Action" functionality). The problem is that you are trying to save the files to a different folder - an Action either saves the files back to the same filename (replacing the original document), or to the same folder, but with a modified filename. To save to a different folder makes things a bit more complex.

Let's assume you have your files in a folder named Documents/MyFiles and you want to save the modified files to Documents/MyNewFiles - the important thing is that you are saving to a folder that is on the same level as your original folder.

Something like this should work:

var fileName = this.documentFileName;
try {
  this.deletePages(1, this.numPages - 1);
} catch (e) {
  console.println(e);
}
this.saveAs("../MyNewFiles/" + fileName);

For this to work, you will have to add one "Execute Javascript" (under "More Tools") to your Action, and then use this script (after making any modifications to adjust it to your specific environment).