diff --git a/crates/ocs_doc_api/IMPLEMENTATION.md b/crates/ocs_doc_api/IMPLEMENTATION.md
index 31bf0bcda..91dc6db3c 100644
--- a/crates/ocs_doc_api/IMPLEMENTATION.md
+++ b/crates/ocs_doc_api/IMPLEMENTATION.md
@@ -68,10 +68,11 @@ variants append at enum end.
   get/set; read-only nested block-content traversal.
 
 ### Phase 4 — paper-space & viewports
-- **Entities:** viewport entities.
-- **Methods:** `create_viewport`, set-view (target, center, scale), layout
-  queries.
-- **Blocked by:** a viewport query model (view target/center/scale DTOs).
+- **Done:** `create_viewport(center, width, height, view_target, view_height)` →
+  `Operation::CreateViewport`; `bounds()` = center ± width/2,height/2; `transform`
+  moves the paper-space center. Covered by `phase4_*` test.
+- **Remaining:** `set_view` (retarget/re-zoom an existing viewport) and a
+  viewport-view query (view target/center/scale DTOs).
 
 ### Phase 5 — media & misc (read-mostly)
 - **Entities:** raster image, underlay, table, light.
diff --git a/crates/ocs_doc_api/examples/common/mod.rs b/crates/ocs_doc_api/examples/common/mod.rs
index e9ec290ab..d01a2aa43 100644
--- a/crates/ocs_doc_api/examples/common/mod.rs
+++ b/crates/ocs_doc_api/examples/common/mod.rs
@@ -105,6 +105,9 @@ impl DocApiBackend for MockBackend {
         }
         Ok(self.alloc("Insert"))
     }
+    fn add_viewport(&mut self, _spec: &ocs_doc_api::ops::ViewportSpec) -> ApiResult<ObjectId> {
+        Ok(self.alloc("Viewport"))
+    }
     fn add_vertex(&mut self, id: ObjectId, _at: usize, _point: [f64; 3]) -> ApiResult<()> {
         if self.entity_exists(id) {
             Ok(())
diff --git a/crates/ocs_doc_api/spec/entities.toml b/crates/ocs_doc_api/spec/entities.toml
index e30563518..7b8de56ed 100644
--- a/crates/ocs_doc_api/spec/entities.toml
+++ b/crates/ocs_doc_api/spec/entities.toml
@@ -252,6 +252,21 @@ name = "create_insert"
 args = [{ name = "block_name", ty = "&str" }, { name = "insert_point", ty = "[f64; 3]" }, { name = "scale", ty = "f64" }, { name = "rotation", ty = "f64" }]
 op = "CreateInsert"
 
+# ============================================================================
+# PAPER-SPACE FAMILY (phase 4) — viewports
+# ============================================================================
+[[family]]
+name = "Viewport"
+acadrust_variant = "Viewport"
+handle = "Entity"
+collection = "entities"
+description = "Paper-space viewport: a width×height window at center looking at view_target with view_height zoom. bounds = center ± w/2,h/2; transform moves center."
+
+[[family.constructor]]
+name = "create_viewport"
+args = [{ name = "center", ty = "[f64; 3]" }, { name = "width", ty = "f64" }, { name = "height", ty = "f64" }, { name = "view_target", ty = "[f64; 3]" }, { name = "view_height", ty = "f64" }]
+op = "CreateViewport"
+
 # ============================================================================
 # Cross-cutting ops (generic handles + bulk) — documented in build.rs
 # ============================================================================
diff --git a/crates/ocs_doc_api/src/backend.rs b/crates/ocs_doc_api/src/backend.rs
index 9be15e0ba..5fc03379e 100644
--- a/crates/ocs_doc_api/src/backend.rs
+++ b/crates/ocs_doc_api/src/backend.rs
@@ -39,6 +39,9 @@ pub trait DocApiBackend {
     /// the fresh `ObjectId`. `Validation` if the block is unknown.
     fn add_insert(&mut self, spec: &crate::ops::InsertSpec) -> ApiResult<ObjectId>;
 
+    /// Add a paper-space `VIEWPORT`; returns the fresh `ObjectId`.
+    fn add_viewport(&mut self, spec: &crate::ops::ViewportSpec) -> ApiResult<ObjectId>;
+
     /// Remove any first-level entity by id. Returns `false` if absent; returns
     /// `Err` if the entity exists but cannot be removed (e.g. locked layer).
     fn remove_entity(&mut self, id: ObjectId) -> ApiResult<bool>;
diff --git a/crates/ocs_doc_api/src/executor.rs b/crates/ocs_doc_api/src/executor.rs
index 4fe69917f..5267229b3 100644
--- a/crates/ocs_doc_api/src/executor.rs
+++ b/crates/ocs_doc_api/src/executor.rs
@@ -183,6 +183,12 @@ pub fn apply_op<B: DocApiBackend>(b: &mut B, op: Operation) -> ApiResult<Receipt
             b.finalize_op();
             OpOutcome::NewId(id)
         }
+        Operation::CreateViewport(spec) => {
+            b.push_undo(name);
+            let id = b.add_viewport(spec)?;
+            b.finalize_op();
+            OpOutcome::NewId(id)
+        }
     };
     Ok(Receipt {
         outcome: Some(outcome),
diff --git a/crates/ocs_doc_api/src/facade.rs b/crates/ocs_doc_api/src/facade.rs
index ea4f73d32..02bb6bbf0 100644
--- a/crates/ocs_doc_api/src/facade.rs
+++ b/crates/ocs_doc_api/src/facade.rs
@@ -464,6 +464,19 @@ pub struct EntityCollection {
 }
 
 impl EntityCollection {
+    /// Create a paper-space `VIEWPORT` (a `width`×`height` viewport at `center`
+    /// looking at `view_target` with `view_height` zoom).
+    pub fn create_viewport(&self, center: [f64; 3], width: f64, height: f64, view_target: [f64; 3], view_height: f64) -> ApiResult<Entity> {
+        let receipt = self.session.apply_op(Operation::CreateViewport(crate::ops::ViewportSpec {
+            center, width, height, view_target, view_height,
+        }))?;
+        let id = receipt
+            .outcome
+            .and_then(|o| o.new_id())
+            .ok_or_else(|| ApiError::Transport("create_viewport returned no id".into()))?;
+        Ok(Entity::new(self.session.clone(), id))
+    }
+
     /// Place a block reference (`INSERT`) for `block_name` (must exist).
     pub fn create_insert(&self, block_name: &str, insert_point: [f64; 3], scale: f64, rotation: f64) -> ApiResult<Entity> {
         let receipt = self.session.apply_op(Operation::CreateInsert(crate::ops::InsertSpec {
diff --git a/crates/ocs_doc_api/src/gen/api_reference.md b/crates/ocs_doc_api/src/gen/api_reference.md
index 201f9e5ac..0447dbbbb 100644
--- a/crates/ocs_doc_api/src/gen/api_reference.md
+++ b/crates/ocs_doc_api/src/gen/api_reference.md
@@ -95,6 +95,14 @@ Block reference. Place an existing BlockRecord by name; transform moves its inse
 
 - **create_insert**(`block_name: &str, insert_point: [f64; 3], scale: f64, rotation: f64`) -> `Entity`
 
+## `Entity` (acadrust `Viewport`, collection `entities`)
+
+Paper-space viewport: a width×height window at center looking at view_target with view_height zoom. bounds = center ± w/2,h/2; transform moves center.
+
+### Constructors (`doc.entities()`)
+
+- **create_viewport**(`center: [f64; 3], width: f64, height: f64, view_target: [f64; 3], view_height: f64`) -> `Entity`
+
 ## Generic methods (every handle)
 
 Every typed handle (`Solid`, `Line`, `Circle`, `Polyline`, `Point`, `Entity`) is a
diff --git a/crates/ocs_doc_api/src/gen/binding_schema.json b/crates/ocs_doc_api/src/gen/binding_schema.json
index 611ca78ca..5999bc28a 100644
--- a/crates/ocs_doc_api/src/gen/binding_schema.json
+++ b/crates/ocs_doc_api/src/gen/binding_schema.json
@@ -194,6 +194,13 @@
       "handle": "Entity",
       "methods": [],
       "name": "Insert"
+    },
+    {
+      "acadrust_variant": "Viewport",
+      "collection": "entities",
+      "handle": "Entity",
+      "methods": [],
+      "name": "Viewport"
     }
   ],
   "layouts": {
diff --git a/crates/ocs_doc_api/src/gen/ops_gen.rs b/crates/ocs_doc_api/src/gen/ops_gen.rs
index 3e7883f3a..7657cb82c 100644
--- a/crates/ocs_doc_api/src/gen/ops_gen.rs
+++ b/crates/ocs_doc_api/src/gen/ops_gen.rs
@@ -6,7 +6,7 @@
 use serde::{Deserialize, Serialize};
 
 use crate::id::ObjectId;
-use crate::ops::{BoolOp, Curve2Spec, EntitySpec, InsertSpec, PlacementSpec, SolidPrimitive};
+use crate::ops::{BoolOp, Curve2Spec, EntitySpec, InsertSpec, PlacementSpec, SolidPrimitive, ViewportSpec};
 
 /// A typed write operation (plan §5). Each variant is ONE atomic host call = one
 /// undo step. Append new variants at the END only.
@@ -29,4 +29,6 @@ pub enum Operation {
     DeleteMany(Vec<ObjectId>),
     // containers
     CreateInsert(InsertSpec),
+    // paper-space
+    CreateViewport(ViewportSpec),
 }
diff --git a/crates/ocs_doc_api/src/ops.rs b/crates/ocs_doc_api/src/ops.rs
index f6ca50ecd..8d3566059 100644
--- a/crates/ocs_doc_api/src/ops.rs
+++ b/crates/ocs_doc_api/src/ops.rs
@@ -67,6 +67,18 @@ pub struct InsertSpec {
     pub rotation: f64,
 }
 
+/// Construction spec for a paper-space `VIEWPORT`: a `width`×`height` viewport
+/// centered at `center` (paper space), looking at `view_target` (model space,
+/// WCS) with `view_height` (model-space height visible; the viewport's zoom).
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct ViewportSpec {
+    pub center: [f64; 3],
+    pub width: f64,
+    pub height: f64,
+    pub view_target: [f64; 3],
+    pub view_height: f64,
+}
+
 /// A rigid similarity (rotation + translation + optional uniform scale/reflection)
 /// as a plain-data mirror of `cadkernel::brep::transform`'s `Placement`
 /// (non-serde). Columns are the new basis axes; `origin` is the translation.
@@ -115,6 +127,7 @@ impl crate::gen::Operation {
             TransformMany { .. } => "TransformMany",
             DeleteMany(_) => "DeleteMany",
             CreateInsert(_) => "CreateInsert",
+            CreateViewport(_) => "CreateViewport",
         }
     }
 }
diff --git a/crates/ocs_doc_api/tests/mock_backend.rs b/crates/ocs_doc_api/tests/mock_backend.rs
index 5de13c856..695539c61 100644
--- a/crates/ocs_doc_api/tests/mock_backend.rs
+++ b/crates/ocs_doc_api/tests/mock_backend.rs
@@ -65,6 +65,9 @@ impl DocApiBackend for MockBackend {
         }
         Ok(self.alloc("Insert"))
     }
+    fn add_viewport(&mut self, _spec: &ocs_doc_api::ops::ViewportSpec) -> ApiResult<ObjectId> {
+        Ok(self.alloc("Viewport"))
+    }
     fn add_vertex(&mut self, id: ObjectId, _at: usize, _point: [f64; 3]) -> ApiResult<()> {
         if self.entity_exists(id) {
             Ok(())
diff --git a/src/app/doc_api.rs b/src/app/doc_api.rs
index e6faf7db2..7935c667e 100644
--- a/src/app/doc_api.rs
+++ b/src/app/doc_api.rs
@@ -125,6 +125,20 @@ impl DocApiBackend for HostSession<'_> {
         Ok(handle_to_obj(handle))
     }
 
+    fn add_viewport(&mut self, spec: &ocs_doc_api::ops::ViewportSpec) -> ApiResult<ObjectId> {
+        use acadrust::entities::Viewport;
+        use acadrust::types::Vector3;
+        let v3 = |p: [f64; 3]| Vector3::new(p[0], p[1], p[2]);
+        let mut vp = Viewport::new();
+        vp.center = v3(spec.center);
+        vp.width = spec.width;
+        vp.height = spec.height;
+        vp.view_target = v3(spec.view_target);
+        vp.view_height = spec.view_height;
+        let handle = self.scene_mut().add_entity(EntityType::Viewport(vp));
+        Ok(handle_to_obj(handle))
+    }
+
     fn add_vertex(&mut self, id: ObjectId, at: usize, point: [f64; 3]) -> ApiResult<()> {
         let handle = obj_to_handle(id);
         let Some(entity) = self.document().get_entity(handle).cloned() else {
@@ -183,6 +197,7 @@ impl DocApiBackend for HostSession<'_> {
                 | EntityType::Ray(_)
                 | EntityType::XLine(_)
                 | EntityType::Insert(_)
+                | EntityType::Viewport(_)
                 | EntityType::Point(_)
                 | EntityType::LwPolyline(_)
         );
@@ -626,6 +641,44 @@ mod tests {
         assert!((r.base_point.z - 5.0).abs() < 1e-6);
     }
 
+    // ── Phase 4: paper-space viewports ───────────────────────────────────────
+
+    #[test]
+    fn phase4_create_viewport_bounds_transform() {
+        let mut app = OpenCADStudio::new_for_test();
+        let mut host = HostSession::new(&mut app, 0);
+        // A 40x30 paper-space viewport at (50,50,0) looking at model origin.
+        let vp = new_id(&dispatch(&mut host, DocApiEnvelope::op(Operation::CreateViewport(
+            ocs_doc_api::ops::ViewportSpec {
+                center: [50.0, 50.0, 0.0], width: 40.0, height: 30.0,
+                view_target: [0.0, 0.0, 0.0], view_height: 100.0,
+            }))).unwrap());
+        let handle = obj_to_handle(vp);
+        let Some(EntityType::Viewport(v)) = host.document().get_entity(handle) else { panic!("viewport not found") };
+        assert!((v.width - 40.0).abs() < 1e-9 && (v.view_height - 100.0).abs() < 1e-9);
+
+        // Bounds = center ± width/2, height/2.
+        let receipt = dispatch(&mut host, DocApiEnvelope::queries(vec![
+            Query::GetEntity { id: vp }, Query::GetBounds { id: vp }])).unwrap();
+        match &receipt.query_results[0] {
+            QueryResult::Entity(e) => assert_eq!(e.kind, "Viewport"),
+            other => panic!("expected entity, got {other:?}"),
+        }
+        match &receipt.query_results[1] {
+            QueryResult::Bounds(b) => {
+                assert!((b.min[0] - 30.0).abs() < 1e-6 && (b.max[0] - 70.0).abs() < 1e-6, "{b:?}");
+                assert!((b.min[1] - 35.0).abs() < 1e-6 && (b.max[1] - 65.0).abs() < 1e-6, "{b:?}");
+            }
+            other => panic!("expected bounds, got {other:?}"),
+        }
+
+        // Transform moves the viewport's paper-space center.
+        dispatch(&mut host, DocApiEnvelope::op(Operation::Transform {
+            id: vp, placement: ocs_doc_api::PlacementSpec::at([10.0, 0.0, 0.0]) })).unwrap();
+        let Some(EntityType::Viewport(v)) = host.document().get_entity(handle) else { panic!("viewport not found") };
+        assert!((v.center.x - 60.0).abs() < 1e-6);
+    }
+
     // ── Phase 3: containers (block references) ───────────────────────────────
 
     #[test]
diff --git a/src/app/doc_api_convert.rs b/src/app/doc_api_convert.rs
index 880507133..87891aa4c 100644
--- a/src/app/doc_api_convert.rs
+++ b/src/app/doc_api_convert.rs
@@ -129,6 +129,11 @@ pub fn transform_entity_geometry(
             ins.insert_point = apply(ins.insert_point);
             EntityType::Insert(ins)
         }
+        EntityType::Viewport(vp) => {
+            let mut vp = vp.clone();
+            vp.center = apply(vp.center);
+            EntityType::Viewport(vp)
+        }
         EntityType::Point(pt) => {
             let mut pt = pt.clone();
             pt.location = apply(pt.location);
@@ -242,6 +247,7 @@ pub fn entity_kind_name(entity: &EntityType) -> &'static str {
         EntityType::Ray(_) => "Ray",
         EntityType::XLine(_) => "XLine",
         EntityType::Insert(_) => "Insert",
+        EntityType::Viewport(_) => "Viewport",
         EntityType::Text(_) => "Text",
         EntityType::MText(_) => "MText",
         _ => "Other",
@@ -311,6 +317,18 @@ pub fn entity_bounds(entity: Option<&EntityType>, id: ObjectId) -> ApiResult<Aab
             }
             Aabb { min, max }
         }
+        EntityType::Viewport(vp) => Aabb {
+            min: [
+                vp.center.x - vp.width / 2.0,
+                vp.center.y - vp.height / 2.0,
+                vp.center.z,
+            ],
+            max: [
+                vp.center.x + vp.width / 2.0,
+                vp.center.y + vp.height / 2.0,
+                vp.center.z,
+            ],
+        },
         // Ray/XLine are unbounded by definition — no finite bounds.
         _ => return Err(ApiError::Unsupported("bounds for this entity family is not yet implemented".into())),
     };