How do I find back documents that I deleted by accident?

If the files aren't still in the trashcan and if there aren't Time Machine or other backups, the costs increase and the likelihood of successful recovery decreases. Backups are the usual path of recovering from this and from similar cases, as otherwise you're attempting to find and undelete a file, and that's marginally possible in the best of cases with older hard disk drives (HDDs) and that so-called disk scavenging is not feasible on Solid State Disks (SSDs) and related storage. And even with hard disk storage and with scavenging, scavenging and undeleting is more likely to work when the system is immediately shut down, and the chances of success of that scavenging decreases as the system continues to operate with the HDD normally; as the system churn through its caches and deleted blocks, and as the deleted storage is reused and overwritten. Modern operating systems using SSDs erase the storage contents on delete, too—the process uses the TRIM command—which means there's no data to scavenging from those, if the data is not still in the trashcan or still on a backup.