Here more details:
1. and 3. The problem is with different PDF files, but only if they have 1 page. It doesn't matter whether the file includes graphics or not.
2. I do receive the file via the mail app functioning perfectly. I can open it via iBooks. But when I open it again from iBooks, or any other app, and send it via mail, the file is broken.
The recipient using Outlook cannot see the file at all (a box with x is shown instead). If the recipient is using an iOS device the PDF is just shown as picture in the email and cannot be saved or opened.
Also, I found out that the problem does not occur, if I save the email from iBooks as draft first, before sending it via mail.
Try a rest: Simultaneously hold down the Home and On buttons until the iPad shuts down. Ignore the off slider if it appears. Once shut down is complete, turn the iPad back on using the On button. In some cases it also helps to double click the Home button and close all apps from the tray before doing the reset.
So far that did not help. I tried out the following already:
1. Reset as described by you. Nothing changed and the problem is the same.
2. Re-installing iOS via iTunes and setting up the iPad as new device (no backup installed). Afterwards the PDF was sent properly, but on the next day the same problem started to happen. Afterwards I deleted all apps which access apples mail function and PDF files (iBooks, adobe reader, documents to go, ithoughts HD) and restarted the iPad several times (point 1) and only installed iBooks. No change. The problem remains.
I guess I have solved the issue, even though the solution is not logical ...
When sending emails I use a personalized signature, which I add to the settings of my iPad. When using the following the error occurs:
Mit freundlichen Grüßen
Company - Name (in bold letters)
If I delete the signature out of the settings the one-page PDF file is correctly sent out.