To find Recoll from Kmenu, enter Kmenu > Utilities > Recoll. Figure 1 shows the Recoll Advanced Search input screen and demonstrates the real power of Recoll.
The default mode from the main screen is self-explanatory.
In the Advanced Search window, to the left of each search term is a pull-down options menu. Figure 1 shows the top search term with this menu open to show you the options. The default setting is all search terms; the other options you would be most likely to use are any search term and filename search. Each of the five menus tells Recoll what to do with a search term. You can use any combination of these menu options with the available search terms.
Put your search terms in the text boxes on the right, and go.
Figure 1 Advanced search
For the This Phrase option, the number selector tells Recoll the minimum number of incidences of each phrase to look for in a target document.(Despite what's shown in Figure 1, the default is 1, not 0.)
The Terms in Proximity operator is basically Boolean NEAR, so the number selector indicates how close you want to come in terms of word adjacency. For instance, a setting of 5 means that keyword1 and keyword2 must be within 5 words of each other to provide a search hit. Set it for 50, and you should be able to find pages with paragraphs in which your search terms appear together.
In the center of the window, on the left, you'll see the check box to "Restrict file types." Checking it activates the document type selection options, and a set of buttons that let you move file types between the two boxes for "Searched file types" and "Ignored file types."
To use document type selection, click the "Restrict file types" check box as shown. Then, in the menu of "Searched file types," highlight all of them with Control+A and use the Sel button to move all of them to the "Ignored file types" list on the right. Then look in the list of document types and find the file types—PDF, for instance—in which you think the object of your search is likely to be. Ctrl+click to select them, and then hit Sel again to move it back into the "Searched file types" box.
At the bottom of the window is an option to "Restrict results to directory subtree." You can use this to type in a "where to search" directory path, but the program runs fast enough that you'll probably spend more time entering the path than what you'd save by restricting the search space to a specific directory tree or subtree.
Once the search is complete, you'll see the search results in the main screen that opened with Recoll (behind the Advanced Search window). To sort the results, open Tools > Sort Parameters (see Figure 2).
Figure 2 In the Recoll main screen showing the search hits, you can open the sort options.
From the Sort Parameters window (Figure 3), there are pull-down menus to sort by file date (shown in the Figure 2 results) or Mime type or both, in ascending/descending order. The default order is ascending; Figure 3 shows descending date order selected.
Figure 3 Sort options
At this point, try some random searches.
Keep in mind that even this advanced search won't find everything. The essential limitation of keyword searching is that we don't always know what the right keywords are, or whether or not a database is really complete.
Enjoy. I think with Recoll you'll find your computer much more useful than it was, particularly if you use it to store your personal/business/academic reference materials.