I took a quick look around but didn't find a "global" answer to a question that I get asked fairly often by new and even seasoned iPad owners...how to attach a file to an email being sent from an iPad.
You can email most anything from an iPad but since iOS doesn't operate on a normal file system like Mac or Windows machines it takes a different path than it does with Mail or Outlook, etc. Basically the general rule is that if you want to email a document of some sort you would do it directly from whatever app you're using at the time rather than using the iPad's Mail program. It sort of make sense when you think about it and works well when you get used to it. it's really a bit easier than opening Mail, opening a new email document, clicking on "Attach" and then searching around for a file...one less step. So it really depends on what you want to email.
If you want to email a document from Office2 HD for instance, open the app, open the Inbox and find the file you want to email. Click on the disclosure button (small blue circle with a forward arrow on the RH side of the document name/file). An "Email file" button appears. Just click on that and a "New Message" email form will appear with the file attached.
Photos are the most common thing folks seem to want to email. There are two ways of doing this depending on how big you want the photo to be. To start open the Photos app, find the photo you want to email, open it full screen and you'll see a little box with an arrow pointing to the right coming out of it in the upper right hand corner of the screen. Tap that and you have several options including "Email Photo". If you tap on "Email Photo" a "New Message" window will appear with the photo attached. Doing it this way will send a reduced resolution copy of the photo (to keep the file size down). If you want a full resolution photo to be sent tap on "Copy Photo", then open your Mail app. Create a new email as usual and then double tap the body of the email. The little options popup menu that includes "Paste" will appear. Tap "Paste" and a full-sized version of the photo will be dropped in.
If you want to send several photos open the Photo app and then the album of photos that includes the ones you want to send. Click on the same little box with the arrow in the toolbar at the top RH of the screen. That changes the screen to "Select Photos". Tapping on a photo will add a blue circled check mark to the thumbnail (tap it again if you decide not to use it and the check mark disappears). Once all of the photos you want to use are chosen click the “email” or "Copy" buttons in the LH corner of the toolbar at the top of the screen. Your photos will be sent directly using the email button or you if you copied them you can then paste them into a new message in the iPad's Mail app.
Otherwise I use GoodReader (highly recommended) to handle and store most of my documents. It's very easy to email from GoodReader. Open the GoodReader app, find the document you want to email and open it. That same little box as Photos uses (little RH arrow pointing out - I'm sure theres a technical name for it!) is on the bottom toolbar. Tap on it and a popup with "Email File" appears. Tap on that and a "Mail with GoodReader attachments" window opens with the file attached.
So that's about it. Others may jump in with some additional ideas or tips but I hope that helps!