You can open an existing text file; copy & paste screen images and strings for translation.
In the Professional Edition, you can also import document files such as WORD, Excel and PDF, with no limit to the length of the document.

You can display the translation as a subscript alongside the source term. You can right click to check for an alternative translation, and change the text displayed.
You can remove the subscript display when you have learned the translation for the term, to help you learn.

You can set your own dictionary URL, by replacing the default dictionary URL that comes with the product.
You can also register Eijiro (purchase necessary), and quickly refer to it as well as your own dictionary.

In the Professional Edition, you can print the translated subscript with the source text, exactly as you see in preview mode.

tango can automatically analyze an English text and display the part of speech, tense, plural and possessive forms of nouns and comparatives.

By setting a bookmark on the next section you wish to resume reading, tango will display the page directly, without the bother of having to scroll.

As you can add terms which may not be in a standard dictionary, or change the translation, you can build your original dictionary suited to your field of expertise.
You will find it very useful to have this kind of dictionary, when you need to read another text in the same field.