You need at least the Demo version of Trados. Here is the solution for Word and RTF files and files processed with S-Tagger (rtf files with a lot of tags).
If you get unsegmented files from your customer (segmented files contain every sentence twice - the source sentence is marked hidden and between the source and the target sentences you have things like <}0{> with varying numbers):
Open Trados WB with the TM from your customer (if you have a proper Trados version) or create a new empty TM in your language pair (if you have the Demo), go Tools, Translate, select the option segment unknown sentences, select the files you need to translate and click on Translate. The result is untranslated, segmented, uncleaned Trados files.
For each file you have now 2 files, one with the original extension (e.g. rtf) and one with the extension BAK, which is a backup of your original.
Close Trados WB.
Create a project in DVX. Select the files you want to import – the ones with the original extension. In the import window of the Wizard highlight all of them and click on the button Properties. Click in the field Filter that shows Microsoft Word or Rich text format (depending on your files). Select Trados Workbench. Now import your files and translate them.
Be careful to check for code errors (CTRL+Shift+F8) before exporting.
After the export, you have uncleaned, translated Trados files.
If you need to clean them, open Trados WB, Tools, Cleanup, select do not update TM and select your translated files, click Cleanup. No you have cleaned files (files with the extension you first had) and uncleaned files with the extension BAK.
If your customer has sent you a TM and you do not have a full Trados version, you need to get the TM as a Trados.txt or TMX export. You cannot do this conversion in the Trados Demo. If you want to import a Trados.txt file into a DVX Database you must select Trados Workbench as import format, even if it is a txt file. If you forget this, you will get a lot of tags you do not want to have in your TM.
If you get Tag Editor files (TTX) and after importing them in to DVX you do not see any segments- the files where not segmented in Trados WB. You need to segment them just as described for the Word files.
<Addition below by Rob Laumen>
After importing the TTX file, you need to use the Rows Selector to switch from All Rows to Unpainted Rows. Then right-click on the translation grid and select Clear All Translations (not to worry: this actually means Clear All Translations *In This View*). Now switch back to All Rows using the Rows Selector. Now that all rows with no matches are empty, Auto-Assemble will work on CTRL/ALT+down (if enabled). On non-empty unpainted rows you would have to press CTRL+A to assemble those segments.
</Addition by Rob Laumen>