Same issue with all Microsoft apps...and our company policy prohibits / disables cloud so now no way of accessing and editing documents on iPad pro!
The problem hasn't been narrowed down enough to pinpoint the culprit.
How is this? Their are other email clients. Try Microsoft outlook. There are other ways of transferring documents than email.
There are lots of ways of moving files.
"Box lets you store all of your content online, so you can access, manage and share it from anywhere. Integrate Box with Google Apps and Salesforce and access Box on mobile devices" Rated the most secure cloud storage by SkyHigh Networks.
You can buy a license to run box one of your servers.
https://www.box.com/
Using iTunes to transfer files:
http://support.apple.com/kb/HT4094?viewlocale=en_US&locale=en_US
"iMazing is the all purpose iOS management software: expand your control over your mobile data beyond what is normally possible, without jailbreaking your device. With iMazing, you can easily browse and manage your backups, extract and print your text messages, or drag and drop songs to your iPhone. To put it simply, iMazing allows you to go way beyond what iTunes offers"
https://imazing.com/
Files Connect -- "Cloud Storage services like Dropbox, MobileMe iDisk, Google Docs/Picasa, Facebook photos, FTP, SFTP, WebDAV ... AFS (Apple File Shares) SMB (Windows shares) protocols"
https://itunes.apple.com/us/app/files-connect/id404324302?mt=8
Windows File server
http://itunes.apple.com/us/app/filebrowser-access-files-on/id364738545?mt=8
Simple Transfer - Wireless Photo & Video Backup, Sync & Share by Rambax, LLC
https://itunes.apple.com/us/app/simple-transfer-wireless-photo/id420821506?mt=8
"The kiteworks mobile file sharing solution provides secure creation, viewing, and sharing of enterprise content on smartphones and tablets while providing IT and security teams the administrative controls to manage user privileges and access rights necessary to ensure enterprise security and compliance." " Includes choice of private cloud on-premise."
http://www.accellion.com/solutions/mobile-enablement/mobile-file-sharing
"Dukto is a simple application that allows you to share files between devices connected to the same (wireless) LAN network."
http://www.tidal.it/?page_id=309&lang=en
http://www.msec.it/blog/?page_id=11
"Transfer files the easy way, just drag & drop the file and we will handle the rest. Like Apple AirDrop, but works and on all major platforms and computers that don't support AirDrop. Apps are available for iOS, OS X, Windows, and Android."
https://itunes.apple.com/us/app/instashare-air-drop-transfer/id576220851?mt=8
You could look into Apple's airdrop.
"To share content with AirDrop, both people need one of these devices using iOS 7 or later, or a Mac with OS X Yosemite"
Use AirDrop to wirelessly share content - Apple Support
iPad to your computer via USB
-- "iExplorer's disk mounting features allow you to use your iPhone, iPod or iPad like a USB flash drive."
http://www.macroplant.com/iexplorer/
-- "GoodReaderUSB is a practical and useful application whose main purpose is to help users transfer files and folders from their mobile device to PC effortlessly. It helps them to move and backup important data from their Apple device via a USB cable."
http://www.softpedia.com/get/IPOD-TOOLS/Multimedia-IPOD-tools/GoodReaderUSB.shtm l
-- How to transfer files from your iPad to your PC with iPad to Computer Transfer
http://www.iphone-mac.com/how-to-transfer-and-sync-contents-from-ipad-to-pc.html