If you'd like to search within the active open document, your browser's built in search will work with the document as well, just like with any other page.
So you can use "Ctrl + F" on windows/linux or "cmd + F" on mac, and it'll show you a little search box, where you can make searches, and it should highlight those in the document.
If you're trying to search all documents for words / parts of words, and say for example trying to find which document contains the word "cat" in it, that is unfortunately not possible, due to encryption/decryption happening in your browser.
All non-encrypted services make these types of searches on the server. So when you type something into the search box, because the server can see the contents of the files, it simply applies the search term to all the files you have, and returns only the results to you. Whereas with Cryptee, because everything is encrypted on your device, and server can't see any of the contents of your files, Cryptee isn't capable of doing this. (in theory it could download all your documents and files, decrypt all of them, and search within these. Would be very impractical, especially with accounts containing lots of documents)
Instead, to alleviate this problem a little bit, Cryptee has inline "tags". These tags are encrypted/decrypted using your key on your device. They are loaded into memory every time you open Cryptee Docs, and allow for instantly searching tags of all documents.
To start adding tags, you can simply type #cat #photos, and these will automatically become tags. Cryptee will remember these once the document is saved.
Then using Cryptee's search box on the top left you can start searching all documents for these tags in real time, and documents containing these tags will show up.
The keyboard shortcut for the search box is : ctrl/cmd + shift + o (short for open), you can start typing, then once the document you wish to open appears you can click or use arrow keys + enter to open it.