A watermark is text or an image that appears either in front of or behind existing document content, like a stamp. For example, you could apply a “Confidential” watermark to pages with sensitive information. You can add multiple watermarks to one or more PDFs, but you must add each watermark separately. You can specify the page or range of pages on which each watermark appears.
Note:
Unlike a stamp, a watermark is integrated into PDF pages as a fixed element. A stamp is a type of PDF comment, which others reading the PDF can open to display a text annotation, move, change, or delete.

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To reuse a watermark and watermark options that you saved in an earlier session, select it from the Saved Settings menu.
To create a text watermark, select Text, and type the text in the box. Adjust the text formatting options as needed.
To use an image as a watermark, select File. Then click Browse and select the image file. If the file has multiple pages with images, specify the Page Number you want.
Note:
Only PDF, JPEG, and BMP images can be used as watermarks.
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To resize the watermark in relation to the original image file size, enter a percentage in the Absolute Scale option (in the Source area of the dialog box).
To resize the watermark in relation to the PDF page dimensions, enter a percentage in the Scale Relative To Target Page (in the Appearance area of the dialog box).
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Note:
If you have multiple watermarks in a PDF, this procedure will update only the first watermark you added and will discard all other watermarks. If you change your mind about updating the watermarks after you have completed this process, immediately choose Edit > Undo Watermark.
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Open a single PDF, or select one or more component PDFs in a PDF Portfolio. Then choose Tools > Edit PDF > Watermark > Remove.
To remove watermarks from multiple PDFs, close any open PDFs and choose Tools > Edit PDF > Watermark > Remove. In the dialog box that appears, click Add Files, choose Add Files, and then select the files. Click OK, and then in the Output Options dialog box, specify your folder and filename preferences.