You don't need TextEdit for this. There is a command line program textutil which will do the job without all the opening and saving stuff required with TextEdit. We can fix your TextEdit script (it has a few errors) but try this first and let us know if it does the job for you. The html files will have the same name but with the html extension and will be located in source_folder. The ouput path can be changed in the code by using the "-output" switch of textutil. See "man textutil" if you want to look at everything it can do.
And a general question... what is a RTD file? Do you mean rtf or rtfd? Textutil will work with rtf/rtfd but not rtd, so I hope that isn't really your file type.
set source_folder to choose folder with prompt "Choose a source folder."
set output_folder to choose folder with prompt "Choose an output folder."
tell application "Finder"
set theFiles to (files of entire contents of source_folder) as alias list
end tell
repeat with aFile in theFiles
tell application "Finder"
set fileName to name of aFile
set fileExt to name extension of aFile
end tell
set outputPath to (output_folder as text) & text 1 thru -((count of fileExt) + 1) of fileName & "html"
do shell script "/usr/bin/textutil -convert html -output " & quoted form of POSIX path of outputPath & space & quoted form of POSIX path of aFile
end repeat
You mention you are new to applescript, so I'll give you some general pointers you should keep in mind when writing applescript code.
- Avoid putting tell blocks of code inside each other. You have tell app TextEdit inside tell app Finder. That's bad. Doing this is a source of many conflicts because you are basically telling the Finder to tell TextEdit to do something. That's not good because commands can get confused and it's really hard to debug these kinds of issues. So keep your tell blocks separate.
- Avoid telling an application to perform a command that is not in its applescript dictionary. You should only tell an application to do commands that it knows and an application only knows about the commands in its dictionary. So for example, you are telling the Finder to "choose folder". The Finder does not know that command. That's an applescript command. So doing as you have done is another possible source of errors. In this case that's a simple command and it will work but in general avoid doing this.
- Regarding the Finder, you should avoid using it too much. The Finder is a major program on your computer and is often busy doing computer related stuff. As such it's best to only use it when necessary. As an example you can see in my code that I removed the "choose folder" and the repeat loop from the Finder. I purposely appended "as alias list" to the end of the Finder command to make the list of files usable outside of the Finder tell block of code. Of course use the Finder if needed but it's best to not use it if you don't need it.
- Use the applescript dictionary of your applications. As mentioned above, the dictionary lists all of the terms and the syntax that an application understands (granted the dictionaries are difficult to understand but you will get better at it the more you use them). Under the file menu of AppleScript Editor choose "Open dictionary" and a list of all the applications that understand applescript is shown. Choose an application from that to see its dictionary. So for example, you are trying to figure out TextEdit's "save as" command. You can usually get good direction from the dictionary so you should take a look at that. Use the search field to search!
So I hope that helps! Good luck.