I use a cloud storage system called 'Microsoft Skydrive'. 25GB of online storage linked to my PC.
I then have apps on my ipad and iphone which will allow me to download whichever document, photo or whatever that I've copied into my 'skydrive' folder on my PC.
On the ipad or iphone you will need an App to open the file, such as 'PDF reader' if your file is a PDF or something else such as Apple 'Pages' (£9.99 I think) if your file is a 'Word' document.
You can then either save it on your ipad, or just open it, send it off then delete it untill the next time you want to download it, keeping your ipad memory free.
If you install an App that allows you to save and open 'Word' documents, you should be able to transfer a file from your PC to the ipad in itunes when you dock your ipad.