If you are trying to send the PDF file as an email attachment using Acrobat Reader app on Android or iOS, then follow the steps below:
On Android device:
Open the PDF in Acrobat Reader.Once you are in 'Viewer' click on the Share icon on the bottom right.
It will give 2 options: 'Share' & 'Share Public link'
Click on 'Share' and from the list that shows up select mail app which you are using.
Under Viewer there is 2nd option at bottom right for Share.
Click on it and you will get about 5 options to choose from.
Select the 1st one, 'Share File'
This will ask you if you want to share file as original or flattened copy.
Choose the option as per your requirement and then you get few more option to choose from,
like Message, Mail, etc.
Select the Mail or any other appropriate app to attach the PDF as an attachment.
I hope this workflow will help you in sending mails with PDF attachments.
Success (using iOS) - many thanks!