I Am Receiving an Error Message when Uploading File in Adobe Sign

Hey guys, I am a the classic beginning user of Adobe Sign. I've never used it once in any capacity and would like to change that. I am currently faced with an issue that I cannot make sense of. As I go through the steps in Acrobat Reader DC to send a PDF to an email, I get an error message (see below). It happens only once I click the "Specify Where to Sign" button, which appears to be the last step in the Adobe Sign process. The ensuing loading bar reaches 60% before the error message appears. I've tried it probably five or so times. Any help is greatly appreciated!