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PDFにオンライン注釈

Add highlights, text, sticky notes, drawings, arrows and shapes to PDF. Files are processed locally in your browser, no upload needed.

🔒Local ProcessingBrowser Local ProcessingNo Registration

Drop PDF here or click to select

Upload a PDF file to start annotating

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Your PDF will not leave this device.

What is PDF Annotation?

PDF annotation is the process of adding marks, comments, highlights and visual notes to an existing PDF document without modifying its original content. It is widely used for document review, proofreading, collaboration and archiving. Qudo's Annotate PDF tool runs entirely in your browser, so your documents never leave your device.

How to Annotate a PDF

  1. Upload your PDF file by dragging it into the upload area or clicking to select.
  2. Choose an annotation tool from the toolbar: highlight, freehand drawing, text, sticky note, stamp, shape or image.
  3. Click or drag on the PDF page to add your annotation. Adjust properties like color, opacity and line width in the right panel.
  4. Navigate between pages using the thumbnail sidebar or page navigation buttons.
  5. When finished, click Export to download the annotated PDF. Annotations are flattened into the PDF for maximum compatibility.

Supported Annotation Types

Qudo supports text highlighting, underline, strikethrough, freehand drawing, text boxes, sticky notes, stamps (Approved, Rejected, Draft, etc.), images, rectangles, circles, arrows and lines. Each annotation type supports custom colors, opacity and size adjustments.

PDF Annotation vs PDF Editing

PDF annotation adds marks on top of existing content without changing the original text, fonts or layout. PDF editing modifies the actual content of the document. This tool is designed for annotation and review, not for editing existing paragraphs or reformatting pages.

PDF Annotation vs Fill and Sign

Fill and Sign is designed for completing forms: adding text to form fields, entering dates, checking boxes and adding signatures. PDF Annotation is designed for reading review: highlighting important passages, circling items, adding notes and review comments. Choose the tool that matches your task.

Why Can't I Select Text in Scanned PDFs?

Scanned PDFs are images of paper documents. They do not contain a text layer, so text cannot be directly selected for highlighting. For scanned PDFs, use the rectangle highlight mode to manually mark areas. For text selection, you would first need to run OCR (Optical Character Recognition) to add a text layer.

Editable vs Flattened Annotations

Flattened annotations are permanently drawn onto the PDF pages, ensuring they look the same in all PDF readers. Editable annotations are stored as separate PDF annotation objects that compatible readers can display and sometimes modify. This tool defaults to flattened annotations for maximum compatibility. Once flattened, annotations cannot be individually modified.

Files and Privacy

Your PDF files and all annotation content are processed entirely within your browser. No files, text content, annotation text, author names or file names are uploaded to any server. When you close the page or click Start Over, all file data and annotations are cleared from memory.

Limitations

This tool cannot modify existing PDF text, fonts or layout. Scanned PDFs require OCR before text can be selected. Very large files (over 200 MB) may cause memory issues on some devices. CJK text export requires font embedding which increases file size. Annotations are flattened on export and cannot be individually edited afterward.

Frequently Asked Questions

Are my PDF files uploaded to a server?▼
No. All processing happens locally in your browser. Your files never leave your device.
Can I highlight text in a scanned PDF?▼
Scanned PDFs do not have a text layer, so you cannot select text directly. Use the rectangle highlight mode to manually mark areas instead.
Can I edit annotations after downloading?▼
Annotations are flattened into the PDF on export, so they become part of the page content. To continue editing, keep your original file and re-annotate.
Do annotations change the original PDF?▼
No. The original file is never modified. A new annotated copy is generated for download.
Does it support Chinese and Arabic text?▼
Yes. Text annotations support Chinese, Japanese, Korean, Arabic (with RTL), English, French, German, Spanish, Portuguese and Russian. CJK fonts are loaded on demand during export.
Can I use this on a phone or tablet?▼
Yes. The tool works on mobile browsers that support WebAssembly. Touch drawing is supported.
Why do annotations look different in other PDF readers?▼
This tool uses flattened annotations, which are drawn directly onto the page. This ensures consistent appearance across all readers. If you need standard PDF annotation objects, you may need a different tool.
Can this tool modify existing PDF text?▼
No. This tool only adds annotations on top of existing content. It cannot edit, delete or reformat the original text, fonts or layout.
What is the difference between Fill and Sign and PDF Annotation?▼
Fill and Sign is for completing forms (adding text to fields, dates, signatures). PDF Annotation is for reviewing documents (highlights, drawings, notes, stamps).
Can I process password-protected PDFs?▼
Yes. If you know the password, you can enter it to open the PDF. The tool does not crack or bypass passwords.

Related Tools

All annotations are processed locally in your browser. No PDF content, annotation text, file names or author names are transmitted to any server. When you close the page or start over, all data is cleared from memory.