E-book readers have been around for a while. The first-generation e-book readers, introduced in the late 1990s, were little more than novelty gadgets. Early e-book readers such as Softbook and Rocket Book, were marred by poor-quality LCD screens and short battery life. The e-book titles available for these devices were also rather limited. However, with the release of the first Amazon Kindle device in 2007, the situation changed and the market for e-book readers expanded. Many devices are now available, including the Kindle, Barnes & Noble's Nook and the Sony Reader. Now people are buying and downloading digital books at a breakneck pace.

There are at least a dozen e-book readers currently on the market or due to be released and it can be difficult to know which one is right for your needs. Different e-book readers offer different advantages and disadvantages and vary depending on what make and model they are. While one may be the exact size you are looking for, it may weigh more than you wish to carry. Be careful to check out each e-book reader's specifications before buying and research thoroughly to ensure that you are buying the right product for your needs. So, if you are going to buy an ebook reader, let us learn the factor you should to consider about. And once you have bought an ebook reader, there is another problem here, for the most portable format for ebook is epub, if you want to read pdf files on ebook reader, you have to convert pdf to epub.

Display
One of the most important things to consider when purchasing an e-book reader is the display screen. The e-book readers currently on the market use either E Ink or an LCD. Reading on an LCD screen is exactly the same as reading on a computer screen. LCD screens can display in color. The downside is that LCD screens can lead to eyestrain and do not display well in natural light. E Ink does not display in color but is closer to the printed page in quality and make it easier to read e-books in natural light.

Content and Storage
The best e-book readers give readers access to thousands of book titles and offer plenty of on-board memory for storage. One of the early advantages of the Amazon Kindle was that it had access to Amazon's online book store. This has changed somewhat with increased competition from other devices as well as Google Editions, Google's vast online e-book library.

Battery Life
Consider how long the battery lasts on an e-reader before it needs recharging. Consumers who spend a lot of time reading or plan to bring an e-reader along on vacations or long commutes, should buy a device that has long battery life.

Other Considerations
When buying an e-book reader, consider price vs. the features you value most. For example, the Nook Color has 8 GB of integrated storage, a mircoSD slot, the ability to access more than two million books and a full-color touch screen display. However, the Nook Color ($249 as of April 2011) also costs nearly twice as much as the lowest-priced Kindle model with an E Ink display. A buyer looking for a e-book reader may not want to pay the additional money for a touch screen and a color LCD that makes it difficult to read books at the beach.

we just have talked about three factor you should to consider when buying an ebook reader, but as to which ebook reader you should to buy is all depends on yourself, for example, if you read the most at night with a booklight then a backlight LCD screen might be the best such as the Apple devices like the iPad or iTouch. If you like to read outside or mainly during the day, the best screens will be the eink screens like the Kindle, nook, Sony, or Kobo.

Additional
We have refer to the format converter above, there is more format converter tools here: free pdf to dxf converter and pdf to dwg freeware.

Now that Apple's iPad has become popular, many users will want to view PDF files on the go. With a brilliant screen, e-books and documents display beautifully on the iPad.

So, do you need a good PDF Reader App to view PDF's on your iPad? If you do not know which pdf reader app is suitable for you, I will tell some good pdf readers for you here.

iBooks
Apple's native e-book reader is perhaps the worst choice for in-depth PDF reading. Although the app recently gained the ability to include PDFs alongside e-books, its features are still severely limited. The interface is the slowest among all the apps we tried, taking up to two seconds for a single page to be rendered (an instantaneous action on better readers), and you have no way to highlight, annotate or copy any of the text from the PDF. The search function works well, giving you access to Wikipedia and Google for a Net search if needed, but it kicks you out of the 'iBooks' app and into Safari instead of doing the search in-app. We'd only recommend 'iBooks' for the most casual of PDF readers.

E-book Readers
iPad e-book reading apps such as iBook, Stanza, Kindle and Nook can handle PDF documents as well as e-book formats. Features on the PDF reader are limited compared to the e-book format, but you can pinch zoom to resize the text for easier reading. Some apps also offer in-app brightness or contrast adjustment so you can set the background and text contrast at a level that is easy on the eyes.

PDF Readers
The iPad App Store is full of PDF readers with various features, including the ability to mark up PDFs or add signatures and fill in forms. Each reader's features are explained in the store's deion, so check out several options before you settle on a specific one. Look for one that allows color and contrast adjustment, one and two-page layout views, zoom and search features.

iAnnotate PDF'
iAnnotate PDF' is like the PhotoshopCS5 to the other apps' MS Paint. In fact, it may suffer from too many features, with a zillion helpful pop-ups for every page and tool. Thankfully, once you've worked your way through the app's myriad options, you can turn off the help windows, and customize the interface within an inch of its life. It sports dynamic highlighting, a pen tool, notes and bookmarks, all of which can be saved to the file so that they can be read in any PDF reader on any device.

Pdf format is popular in many areas, not only on ipad but also many other device, especially useful to engineer, they usually need to convert their works to pdf files and then share them with their customers, but when their customers are not satisfied with their work, they have to edit it, the question is that pdf is not editable, how can the engineer do? One way is to convert pdf to dxf with the pdf to dxf freeware. Or they can also convertpdftodwg and then edit them.