I want to search for let's say
*.doc from all my files in Google Drive but I want to exclude results from a certain folder let's say
old docs. What do I type in?
type "-foldername" this will exclude anything named foldername from the search results.
for more options check out search options page
You could rename the files that you don't want to show up in search with a unique string of characters of your choice and filter out those files. For example, if I only want complete documents and not "blank" documents, which for me are templates, I can use "-blank" (minus blank) to filter out documents with "blank" in their titles. I don't think there is a way to rename multiple files at a time in Google drive, but you could download the whole folder once to a computer and then bulk rename them, adding the string of characters you want to filter out. Then you could upload them again to Google drive and delete the originals so they don't show up in search.
What I test, this search all text document in your Drive.
It is what you need?
There is more operators which you can use in Drive (under plus with text "Advance search option"). https://support.google.com/drive/answer/2375114?hl=en
EDIT (after Eight Days of Malaise reaction): Filtering by folder name is not possible in GDrive. Maybe use desktop synchronization app and after that use Explorer searching or some utility.