Searching for text in a file

you could put your code for loading the file and reading the file into a thread. This might make the performance better.
I am not sure if you can search a file without open and reading from it.

Use the TFindDialog component.  The help file describe it use pretty well.

There is no way to search through data except one item at a time, from the first likely place to the last. The fastest method I can think of is to seek for just one character - just the first in the seek string - and when that is found, check if the next few characters in the file match the rest of the seek string.
You may also find it helpful to load as large an amount of data as possible at one time, if there is a lot to be searched through. Disk access is a timewaster, so loading small buffers as needed slows things down. If you're working with many small files, as long as they are all together in sequence on the disk, you could load several into one buffer.
Lastly, if speed is really imortant, then consider using delphi's Assembler to get the repetetive tasks, like the search loop, done more rapidly. This way there is nothing unnecessary going on behind the scenes.

Thanks Pierre! Sorry for being late

Glad I could help