For sending files via e-mail, PDF Expert uses the standard email composer, and when you tap Mail, all operations are made via the Mail app tools.
If the email is not sent and is stuck in the Outbox folder of the Mail app:
To use any other mail app (e.g. Outlook mail app) to send documents from PDF Expert, open the file in PDF Expert > tap the More (Three dots) button in the top right corner > Share > Choose the file format > Select the app you would like to use.
