"How to annotate PDFs on various platforms including Mac, Windows, iPhone, and iPad, both for free and using specific software."

 You can write on a PDF document using various methods depending on the device and software you have access to. Here are some common methods for writing on a PDF:

**1. Adobe Acrobat Reader (Windows and Mac):**

- Open the PDF file using Adobe Acrobat Reader.

- Click on the "Tools" tab in the upper-left corner.

- Select "Fill & Sign."

- Choose the "Add Text" tool.

- Click on the area of the PDF where you want to add text.

- Start typing to add your text. You can also adjust the font size, color, and alignment.

**2. Preview (Mac):**

- Open the PDF file using the Preview app on your Mac.

- Click on the "Markup" toolbar button (it looks like a toolbox).

- Select the "Text" tool.

- Click on the PDF where you want to add text.

- Start typing to add your text.

**3. Online PDF Editors:**

There are several online tools that allow you to write on PDFs without installing software. Some popular options include:

- Smallpdf

- PDFescape

- Sejda

Here's a general process for using these online tools:

- Go to the website of your chosen online PDF editor.

- Upload your PDF file.

- Use the provided tools to add text, draw, or annotate the PDF.

- Save the edited PDF to your computer.

**4. Mobile Devices (iPhone and iPad):**

- Use the built-in Markup feature on your iOS device:

  - Open the PDF using the Files app or another PDF viewer app.

  - Tap the Markup button (it looks like a pencil tip).

  - Select the "Text" tool and tap where you want to add text.

  - Start typing.

**5. Windows 10 or 11 (Touchscreen Devices):**

- Open the PDF file using the "Microsoft Edge" browser.

- Click on the "Make a Web Note" button in the toolbar.

- Use the pen or highlighter tool to write on the PDF.

**6. Third-Party PDF Software:**

If you have third-party PDF editing software, such as Adobe Acrobat Pro or Foxit PhantomPDF, you can use their editing features to write on PDFs.

Please note that while many of these methods allow you to add text and annotations to a PDF, some advanced PDF editing features (e.g., editing existing text) may require premium software or a subscription.

Remember to save your edited PDF once you've made your changes. Always make a backup of the original PDF if you want to preserve the original content.