I don't know if the following is what you expected to get here, but...
Your examples would be translated to:
I have attached the document in this mail - Ich habe das Dokument an die E-Mail angehängt. (not the best phrase) or Ich habe das Dokument der E-Mail beigefügt. (a bit better)
Please find the document attached with this mail - Bitte beachten Sie das Dokument im Anhang der E-Mail. or Bitte entnehmen Sie das Dokument dem Anhang der E-Mail.
As often there is not only ONE solution. You already noticed that it is difficult to decide what phrase would fit best. You could also say Die Informationen können Sie dem Dokument im Anhang entnehmen.
In most cases it depends on the context. It is also possible to elegantly combine that particular piece of information with an existing sentence, e.g. [...], wie im Anhang ersichtlich. and so on.
Since it is a matter of practice your choice to look for business german training is a good one. i opened google and found some resources that might be helpful:
1.
title: "Geschäftsdeutsch: An Introduction to Business German"
author: Gudrun Clay
publisher: McGraw-Hill
ISBN: 0070113343
GTIN: 09780070113343
2.
title: "Business Etikette in Deutschland"
authors: Joachim Graff & Gretchen Schaupp
publisher: Co.in Medien
ISBN: 978-3-940574-38-1
3.
title: "Business-Etikette für Fortgeschrittene: So bewegen Sie sich
sicher auf jedem Parkett"
authors: Alexander von Fircks, Agnes Anna Jarosch
publisher: Frankfurter Allgemeine Buch
ISBN: 978-3899811780
4.
title: "Business-Knigge: Die 100 wichtigsten Benimmregeln"
authors: Anke Quittschau, Christina Tabernig
publisher: Haufe Lexware
ISBN: 978-3648072424
Also, there are some websites that might be helpful:
http://www.dw.com/en/learn-german/marktplatz/s-2555
http://www.businessgerman.com/de/
http://www.business-knigge.com/
wishing you success and best results :)