diff --git a/docs/guides/form-design.md b/docs/guides/form-design.md
index 1b798e4..4e0a302 100644
--- a/docs/guides/form-design.md
+++ b/docs/guides/form-design.md
@@ -637,7 +637,7 @@ Records audio using device microphone.
 **Expected Schema:**
 ```json
 {
-  "type": "string",
+  "type": "object",
   "format": "audio",
   "title": "Voice Note"
 }
@@ -670,7 +670,7 @@ Records video using device camera.
 **Expected Schema:**
 ```json
 {
-  "type": "string",
+  "type": "object",
   "format": "video",
   "title": "Instructional Video"
 }
@@ -699,12 +699,12 @@ Records video using device camera.
 
 ### File Selection
 
-Allows users to select files from device storage.
+Allows users to pick an arbitrary file from device storage (documents, exports, etc.). Behaves like other **attachment** fields: the observation stores a **basename** (stable key under app `attachments/`) plus portable metadata; the binary syncs through the attachment pipeline separately from the observation JSON.
 
 **Expected Schema:**
 ```json
 {
-  "type": "string",
+  "type": "object",
   "format": "select_file",
   "title": "Upload Document"
 }
@@ -719,15 +719,15 @@ Allows users to select files from device storage.
 ```
 
 **Renderer Behavior:**
-- Opens device file picker
-- User selects file from storage
-- Stores file reference and metadata
-- File is uploaded as attachment
+- Opens the system file picker
+- Copies the file into **`attachments/draft/`** with a generated basename (mobile)
+- Persists **`filename`** (basename), **`timestamp`**, and **`metadata`** (`mimeType`, `size`, `extension`, optional **`originalFileName`** for display)
+- Shows **only the display filename** in the form (no thumbnail or inline preview)
 
 **Platform Constraints:**
-- File type restrictions depend on platform
-- Large files may take time to upload
-- Storage permissions required
+- Allowed file types depend on OS picker and Formulus configuration
+- Large files affect sync time and storage
+- Storage / privacy permissions depend on platform
 
 ### QR Code / Barcode Scanner
 
@@ -1031,7 +1031,7 @@ Show field when boolean is true:
 
 ### Multimedia Capture
 
-Forms can include fields for capturing photos, audio, and video. These are handled as attachments and synchronized separately from observation metadata.
+Forms can include fields for capturing photos, audio, and video, and for attaching generic files (`select_file`). These binaries are handled as **attachments** and synchronized separately from observation metadata (observation JSON holds basename + metadata).
 
 ### Location Capture
 
diff --git a/docs/reference/form-specifications.md b/docs/reference/form-specifications.md
index 5261159..07145e4 100644
--- a/docs/reference/form-specifications.md
+++ b/docs/reference/form-specifications.md
@@ -282,9 +282,11 @@ See the full schema options and examples in [Custom Extensions](../guides/custom
 
 #### File Selection
 
+Generic attachment via document picker. Use **`type: object`** with **`format: select_file`** (Formplayer stores basename + portable metadata; no inline preview).
+
 ```json
 {
-  "type": "string",
+  "type": "object",
   "format": "select_file",
   "title": "Upload Document"
 }
diff --git a/docs/reference/formplayer-contract.md b/docs/reference/formplayer-contract.md
index 62d5836..4271dc2 100644
--- a/docs/reference/formplayer-contract.md
+++ b/docs/reference/formplayer-contract.md
@@ -558,13 +558,13 @@ All custom formats are registered in Ajv and have corresponding custom renderers
 | `gps` | `string` or `object` | `GPSQuestionRenderer` | GPS coordinates |
 | `signature` | `object` | `SignatureQuestionRenderer` | Signature pad |
 | `qrcode` | `string` or `object` | `QrcodeQuestionRenderer` | Barcode scanner |
-| `audio` | `string` or `object` | `AudioQuestionRenderer` | Audio recording |
-| `video` | `string` or `object` | `VideoQuestionRenderer` | Video recording |
-| `select_file` | `string` or `object` | `FileQuestionRenderer` | File picker |
+| `audio` | `object` | `AudioQuestionRenderer` | Audio recording |
+| `video` | `object` | `VideoQuestionRenderer` | Video recording |
+| `select_file` | `object` | `FileQuestionRenderer` | Generic file attachment (picker) |
 
 ### Format Registration
 
-**Ajv Registration** (App.tsx:544-551):
+**Ajv Registration** (App.tsx):
 ```typescript
 ajv.addFormat('photo', () => true);        // Accepts any value
 ajv.addFormat('qrcode', () => true);
@@ -608,6 +608,27 @@ export const customRenderers = [
 }
 ```
 
+**File (`select_file`):**
+
+Use `type: object` with `format: select_file`. The Formplayer stores **basename-only** attachment keys and portable metadata (mime type, size, extension, optional original picker display name). The native app copies the picked file into **`attachments/draft/`** (same layout as photos). The UI shows the **filename only**—there is no embedded preview.
+
+```json
+// Schema
+{
+  "supporting_doc": {
+    "type": "object",
+    "format": "select_file",
+    "title": "Supporting document"
+  }
+}
+
+// UI Schema
+{
+  "type": "Control",
+  "scope": "#/properties/supporting_doc"
+}
+```
+
 **GPS:**
 ```json
 // Schema (string format)
@@ -638,7 +659,7 @@ export const customRenderers = [
 **Key Points:**
 - ✅ No special UI schema required (standard `Control` is sufficient)
 - ✅ Format must be specified in schema
-- ✅ Type can be `string` or `object` (depends on format)
+- ✅ Attachment-backed builtins (**`photo`**, **`audio`**, **`video`**, **`select_file`**) use **`type: object`** in current Formplayer (match JSON Forms testers in `App.tsx`). Other formats may accept `string` or `object` (e.g. **`gps`**, **`qrcode`**).
 - ✅ Custom renderer handles all UI and interaction
 
 ---
diff --git a/docs/reference/formplayer.md b/docs/reference/formplayer.md
index 66c7c42..3d40272 100644
--- a/docs/reference/formplayer.md
+++ b/docs/reference/formplayer.md
@@ -439,7 +439,7 @@ Formplayer includes core question type renderers:
 - `SignatureQuestionRenderer`: Digital signature
 - `AudioQuestionRenderer`: Voice recording
 - `VideoQuestionRenderer`: Video recording
-- `FileQuestionRenderer`: File attachment
+- `FileQuestionRenderer`: Generic file attachment (`format: select_file`, `type: object`) — document picker, basename persistence like photos; **filename-only** UI (no preview)
 - `SubObservationQuestionRenderer`: Embedded sub-observation repeats (`format: sub-observation`) — nested `openFormplayer` with `subObservationMode`
 
 ### Custom Renderers