Indd files are those created with Adobe InDesign. Adobe InDesign is a design program that is used for design work such as posters, brochures, manuals, magazines, books, etc.
When a client sends its material in indd files, it is processed in a somewhat more complex manner than when the material is made in simpler programs like MS Word, Excel, etc.
First, you have to process files, so that translators can work with them in specific translation programs; it is not very common to translate directly in the indd files themselves.
Translation programs used for these formats are very good in terms of respecting the text layout, font color, alignment, etc. However, typical differences between the source language and target language (such as text expansion) it is necessary that you include a graphic editing stage for indd files once they are translated.
This DTP stage is even more necessary if the client needs to see clean files, if it wants the translation to be a mirror of the original file.
And even more necessary, if the client also needs a high resolution PDF file of the same indd ready to go to press.
InDesign supports a wide variety of graphic formats such as TIFF, GIF, JPEG, and BMP, as well as vector formats like EPS.
Even, sometimes, there is also text to translate in these images, that the translator will provide the translated text to the DTP worker, and he will be making the images again in the target language.
So in order to achieve a high quality PDF, not just export to PDF, but you have to link all the fonts, images and any other link in the source material, in order to turn out a complete PDF.
That is why always when you submit a request for translation, it is important to fully understand the needs of the client, to avoid confusion during the process later and to know what is expected as a finished work, and then be quoted on that goal and work.