PDF Annotations

Platform PDF annotation & page-object editing

Android can natively edit PDF annotations since API 36.1 — before that the platform story was render-only and the docs still say so: the Jetpack viewer guide's PDF surface is PdfViewerFragment, which explicitly does not support edit mode and hands annotation off to other apps via an android.intent.action.ANNOTATE intent [kb://android/develop/ui/views/layout/pdf/implement-pdf-viewer]. Do not conclude "use a third-party library" for annotation work before applying the version gate below.

The version gate (decide the entry point first)

Two parallel renderers expose the same editing surface (android.graphics.pdf.component):

Gate at runtime with SdkExtensions.getExtensionVersion(Build.VERSION_CODES.S) [kb://android/guide/sdk-extensions/index]. Extension 18 reaches back to API 31 via mainline updates, so PdfRendererPreV is the branch that covers most devices.

The workflow: open → edit → write

// The fd must be seekable — pipes/sockets are rejected at construction.
ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY).use { fd ->
    PdfRenderer(fd).use { renderer ->                    // or PdfRendererPreV on the ext-18 branch
        renderer.openPage(0).use { page ->
            // Only SUPPORTED annotation types are listed. The pairs are
            // android.util.Pair — NO Kotlin destructuring (no component1/2);
            // read them with .first / .second.
            val existing = page.getPageAnnotations()
            val staleId: Int? = existing.firstOrNull { it.second is FreeTextAnnotation }?.first

            val highlight = HighlightAnnotation(boundsList)   // List<RectF> quads
            val id = page.addPageAnnotation(highlight)
            check(id != -1) { "annotation rejected" }         // add returns -1, it does NOT throw

            highlight.color = newColor
            page.updatePageAnnotation(id, highlight)          // by id -> Boolean success
            staleId?.let { page.removePageAnnotation(it) }    // by id, not list position
        }
        // Write BEFORE close(), to a separate writable fd; the boolean is
        // removePasswordProtection (IOException if true and the doc stays encrypted).
        ParcelFileDescriptor.open(
            dest,
            ParcelFileDescriptor.MODE_READ_WRITE or ParcelFileDescriptor.MODE_CREATE,
        ).use { out ->
            renderer.write(out, false)
        }
    }
}

Contracts:

• addPageAnnotation returns the annotation id, or -1 when the annotation cannot be added — check the return; only null/UNKNOWN-type/already-attached arguments throw (IllegalArgumentException).
• An annotation instance is single-attach document-wide: adding one that is "already added in this page or some other page" throws. Construct a fresh component object per add; don't reuse a removed one across pages.
• Ids, not list positions, drive update/remove. getPageAnnotations() returns only annotation types the API models, so a page with unsupported annotations has gaps — the Pair.first id is the stable handle.
• One page open at a time — the pre-existing PdfRenderer invariant ("you can have only a single page opened at any given time") still applies; close the page before opening the next.
• write() before close(), destination must be a distinct writable seekable fd; IllegalStateException after close.
• The pairs are android.util.Pair, not kotlin.Pair — Kotlin destructuring (for ((id, a) in …)) does not compile against them; use .first/.second.

Rendering what you edited

Annotation types render only when RenderParams.renderFlags includes them: FLAG_RENDER_TEXT_ANNOTATIONS / FLAG_RENDER_HIGHLIGHT_ANNOTATIONS (and the 36.1 additions FLAG_RENDER_FREETEXT_ANNOTATIONS / FLAG_RENDER_STAMP_ANNOTATIONS). An added stamp or free-text that "doesn't show up" in your preview bitmap is usually a missing render flag, not a failed add — re-render with the matching flags set via RenderParams.Builder.setRenderFlags(...) and the render(bitmap, clip, transform, params) overload. The render-mode constants live on RenderParams (and legacy PdfRenderer.Page) — PdfRendererPreV.Page has none, so on the PreV branch write RenderParams.Builder(RenderParams.RENDER_MODE_FOR_DISPLAY); qualifying it via PdfRendererPreV.Page does not compile.

Component vocabulary (android.graphics.pdf.component)

• HighlightAnnotation(List<RectF>) — quad list, one rect per highlighted run.
• FreeTextAnnotation(RectF, String) — bounds + text; text/background colors settable.
• StampAnnotation(RectF) — a container: only PdfPagePathObject, PdfPageTextObject, or PdfPageImageObject children (addObject), per the class contract.
• Page objects also attach directly to the page (addPageObject / getPageObjects / updatePageObject / removePageObject — same id-based contract as annotations), and carry a transform matrix (PdfPageObject.setMatrix/transform). PdfPagePathObject stroke defaults to opaque black in sRGB.
• Page.getTopPageObjectAtPosition(PointF, …) hit-tests the topmost object — use it for tap-to-select before update/remove.

Out of scope (route elsewhere)

Creating PDFs from scratch (PdfDocument canvas API), form filling (applyEdit, API 35), text extraction/search, and embedding a viewer UI (PdfViewerFragment — display-only [kb://android/develop/ui/views/layout/pdf/implement-pdf-viewer]) are separate surfaces; third-party SDKs remain the answer only below the version gate or for annotation types the component API doesn't model.