I found that I have deleted very important file. It was deleted BEFORE Active@ File Recovery was installed on my computer. Is it possible to restore the file?
Yes, if the file has not already been written over (by some other files).
If you have found that some important file is deleted, download and install Active@ File Recovery and search for this file.
It may be a good idea to avoid excessive disk activity on this particular hard drive, not to make a lot of other file deletions, to avoid computer reboots, not to invoke large number of programs concurrently (which would cause the increased OS Paging/Swapping activity), etc. - all of this might overwrite or partially overwrite the deleted document and also will make finding a particular file more complicated.
The more free hard drive space you have on your computer, the greater the chances for a successful retrieval of deleted file contents.
It is always a good idea to extract and install Active@ File Recovery to some OTHER hard drive - that does not contain important deleted file(s).