diff --git a/apps/api/src/htmlreports/html-reports.service.ts b/apps/api/src/htmlreports/html-reports.service.ts
index a07a187..1e39ee3 100644
--- a/apps/api/src/htmlreports/html-reports.service.ts
+++ b/apps/api/src/htmlreports/html-reports.service.ts
@@ -24,7 +24,8 @@ export function parseHtmlValues(def: HtmlReportDef, raw: Readonly<Record<string,
   const missing: string[] = [];
   for (const p of def.params) {
     const v = raw[p.name];
-    let text = typeof v === 'string' ? v.trim() : typeof v === 'number' ? String(v) : '';
+    // un parámetro de solo lectura vale siempre su valor por defecto, escriba lo que escriba el cliente
+    let text = p.readOnly ? '' : typeof v === 'string' ? v.trim() : typeof v === 'number' ? String(v) : '';
     if (text === '') text = p.defaultValue ?? '';
     if (text === '') {
       if (p.required) missing.push(p.label);
diff --git a/apps/api/src/htmlreports/html-reports.spec.ts b/apps/api/src/htmlreports/html-reports.spec.ts
index 381325d..9de2479 100644
--- a/apps/api/src/htmlreports/html-reports.spec.ts
+++ b/apps/api/src/htmlreports/html-reports.spec.ts
@@ -48,11 +48,18 @@ describe('registro de reportes HTML', () => {
     expect(() => validateHtmlReports([{ ...def, params: [P({ name: 'a' }), P({ name: 'a' })] }])).toThrow(/repite el parámetro/);
     expect(() => validateHtmlReports([{ ...def, template: '../fuera.njk' }])).toThrow(/dentro de la carpeta/);
     expect(() => validateHtmlReports([{ ...def, template: '/etc/passwd' }])).toThrow(/dentro de la carpeta/);
+    expect(() => validateHtmlReports([{ ...def, params: [P({ name: 'papel', readOnly: true })] }])).toThrow(/solo lectura y necesita un valor por defecto/);
     expect(validateHtmlReports([def])).toHaveLength(1);
   });
 });
 
 describe('valores de los parámetros', () => {
+  it('un parámetro de solo lectura vale siempre su valor por defecto, aunque el cliente mande otro', () => {
+    const fijo = { ...def, params: [P({ name: 'papel', label: 'Papel', kind: 'select', options: [{ value: 'Carta', label: 'Carta' }, { value: 'A4', label: 'A4' }], defaultValue: 'Carta', readOnly: true })] };
+    expect(parseHtmlValues(fijo, {})).toEqual({ papel: 'Carta' });
+    expect(parseHtmlValues(fijo, { papel: 'A4' })).toEqual({ papel: 'Carta' });
+  });
+
   it('exige los obligatorios, aplica el valor por defecto y comprueba tipos', () => {
     expect(parseHtmlValues(def, { doc: '144153', cantidad: 6 })).toEqual({ doc: '144153', cantidad: '6', papel: 'Carta', fecha: '' });
     expect(() => parseHtmlValues(def, { cantidad: '6' })).toThrow(/Falta indicar: Entrega/);
diff --git a/apps/api/src/htmlreports/html-reports.ts b/apps/api/src/htmlreports/html-reports.ts
index f9d40b8..6a65a4e 100644
--- a/apps/api/src/htmlreports/html-reports.ts
+++ b/apps/api/src/htmlreports/html-reports.ts
@@ -16,6 +16,7 @@ export function validateHtmlReports(reports: readonly HtmlReportDef[]): readonly
     for (const p of r.params) {
       if (names.has(p.name)) throw new Error(`El reporte ${r.code} repite el parámetro ${p.name}`);
       names.add(p.name);
+      if (p.readOnly && !p.defaultValue) throw new Error(`El parámetro ${p.name} de ${r.code} es de solo lectura y necesita un valor por defecto`);
     }
   }
   return reports;
diff --git a/apps/web/src/app/features/reports/report-param-field.spec.ts b/apps/web/src/app/features/reports/report-param-field.spec.ts
index 6a5dafd..871f468 100644
--- a/apps/web/src/app/features/reports/report-param-field.spec.ts
+++ b/apps/web/src/app/features/reports/report-param-field.spec.ts
@@ -60,6 +60,15 @@ describe('ReportParamField', () => {
     expect(select.value).toBe('2');
   });
 
+  it('un parámetro de solo lectura se ve con su valor pero no se puede cambiar', async () => {
+    await show(param({ kind: 'select', label: 'Papel', options: [{ value: 'Carta', label: 'Carta' }], readOnly: true }), 'Carta');
+    const select = el().querySelector('select') as HTMLSelectElement;
+    expect(select.value).toBe('Carta');
+    expect(select.disabled || select.hasAttribute('readonly') || select.closest('[readonly]') !== null).toBe(true);
+    await show(param({ label: 'Nombre', readOnly: true }), 'fijo');
+    expect(inputs()[0].readOnly).toBe(true);
+  });
+
   it('un rango pide desde y hasta y los emite como lista', async () => {
     await show(param({ kind: 'date', range: true }), ['2026-01-01', '2026-01-31']);
     expect(labels().join(' ')).toContain('desde / hasta');
diff --git a/apps/web/src/app/features/reports/report-param-field.ts b/apps/web/src/app/features/reports/report-param-field.ts
index dc53b4c..67d00aa 100644
--- a/apps/web/src/app/features/reports/report-param-field.ts
+++ b/apps/web/src/app/features/reports/report-param-field.ts
@@ -24,23 +24,23 @@ const asList = (v: Value): readonly string[] => (typeof v === 'string' ? (v ===
       @case ('single') {
         @switch (p.kind) {
           @case ('number') {
-            <sbo-number-field [label]="p.label" [required]="p.required" [value]="num(single())" (valueChange)="value.set($event === null ? '' : '' + $event)" />
+            <sbo-number-field [label]="p.label" [required]="p.required" [readonly]="!!p.readOnly" [value]="num(single())" (valueChange)="value.set($event === null ? '' : '' + $event)" />
           }
           @case ('date') {
-            <sbo-date-field [label]="p.label" [required]="p.required" [value]="single()" (valueChange)="value.set($event)" />
+            <sbo-date-field [label]="p.label" [required]="p.required" [readonly]="!!p.readOnly" [value]="single()" (valueChange)="value.set($event)" />
           }
           @case ('select') {
-            <sbo-select-field [label]="p.label" [required]="p.required" [options]="p.options ?? []" placeholder="" [value]="single() || null" (valueChange)="value.set($event === null ? '' : '' + $event)" />
+            <sbo-select-field [label]="p.label" [required]="p.required" [readonly]="!!p.readOnly" [options]="p.options ?? []" placeholder="" [value]="single() || null" (valueChange)="value.set($event === null ? '' : '' + $event)" />
           }
           @case ('lookup') {
             @if (catalog(); as c) {
-              <sbo-lookup-field [label]="p.label" [required]="p.required" [lookup]="c.lookup" resolveOnLeave [value]="single()" (valueChange)="value.set($event)" />
+              <sbo-lookup-field [label]="p.label" [required]="p.required" [readonly]="!!p.readOnly" [lookup]="c.lookup" resolveOnLeave [value]="single()" (valueChange)="value.set($event)" />
             } @else {
-              <sbo-text-field [label]="p.label" [required]="p.required" [value]="single()" (valueChange)="value.set($event)" />
+              <sbo-text-field [label]="p.label" [required]="p.required" [readonly]="!!p.readOnly" [value]="single()" (valueChange)="value.set($event)" />
             }
           }
           @default {
-            <sbo-text-field [label]="p.label" [required]="p.required" [placeholder]="p.placeholder ?? ''" [value]="single()" (valueChange)="value.set($event)" />
+            <sbo-text-field [label]="p.label" [required]="p.required" [readonly]="!!p.readOnly" [placeholder]="p.placeholder ?? ''" [value]="single()" (valueChange)="value.set($event)" />
           }
         }
       }
diff --git a/libs/sap-types/src/gateway.ts b/libs/sap-types/src/gateway.ts
index 16615d4..97c87b6 100644
--- a/libs/sap-types/src/gateway.ts
+++ b/libs/sap-types/src/gateway.ts
@@ -20,6 +20,8 @@ export interface GatewayParam {
   /** Se admiten varios valores. */
   multiple?: boolean;
   defaultValue?: string;
+  /** Se muestra pero no se edita: vale siempre su valor por defecto (por ejemplo el papel de unas etiquetas precortadas). */
+  readOnly?: boolean;
   placeholder?: string;
   /** Opciones de una lista fija (`kind = select`). */
   options?: { value: string; label: string }[];