Gmail is used to send an email where you can type the matter as well as the attached files. It is mostly used in industries to send any documents or any email, etc. If you are not able to attach the file, then you should confirm the internet connection is good and also confirm the location of that file in your device. Simply tap on that file and drag and drop the file on your email. If you are still troubled the same, then you can contact us or Speak To Live Person at Google. www.customer-service-phonenumber.com/gmail-customer-service-number/