Technical documents are files and papers which contain information about advanced pre-War technologies. As such, they are especially valued by the Brotherhood of Steel who seek to stockpile these documents to learn the technologies and prevent the masses from abusing them. They can be turned in to Proctor Quinlan for 25 caps each.
Once the quest Getting Technical is started, technical documents can be found randomly in various containers, they will not appear until this quest is activated.
If the Sole Survivor is an enemy of the Brotherhood, or the Brotherhood has been destroyed, then the option to turn in technical documents for 25 caps each will no longer be available. They may still be collected and sold to other vendors for 1 cap each.