Search Query / Reading Multiple Text Files

i'm currently making a client database program for work that stores data in multiple text files (so that the information won't be confused as to which info belongs to who in the database). Each client has his/her own text file, which isn't really a problem although i realize it's a bit messy. A listbox holds items, each item a person's name.When the listbox selected index is changed, the streamreader opens the corresponding textfile, which is as such: "John Doe.txt", and populates the correct textboxes with the information stored in "John Doe.txt".What I'm unfamiliar with is implementing a search function.

1. search query entered

2. streamreader reads through all txt files in a directory looking for matching keywords.

3. if a match is found in a txt file, it looks at the name ("John Doe.txt"), gets the corresponding listboxitem, and finally, once the textboxes have been populated with the info in the file, highlights the matching keywords.

4. then i figured if there was more than 1 match over more than 1 txt file, you could repeat the process and skip to the next match via the tab key (like the find feature of a WebBrowser or other such application).

What i don't understand is how to read multiple text files, search in keywords, highlight the matching keywords, or the tab function..I know that's a lot to ask on a forum, but I had nowhere else to turn.