The Add Watermark tool loops over every page in pdfDoc.getPages() and draws the watermark on each one, with no option to exclude specific pages.
Acrobat's watermark dialog offers a Page Range Options control to apply a watermark to the whole document or a chosen range. Add watermarks to PDFs in Acrobat on desktop | Adobe Acrobat
Add WatermarkWatermark Every Page PDF
The Add Watermark page only allows uploading a single PDF at a time, so the watermark applies within that one document.
Pick the multi-page PDF you want stamped throughout.
Select the watermark text or image file.
Adjust the opacity and rotation settings.
Click the process button to generate the watermarked document.
Checking Watermark Placement on All Pages
Open the downloaded PDF file.
Scroll through the document to view each page.
Confirm the watermark appears on the first page.
Confirm the watermark appears on the last page.
Continue with Add Watermark Gray Color Fixed or Add Watermark Opacity Transparency.
Frequently Asked Questions about Watermark Every Page PDF
Can I skip the watermark on a specific page?
Split the document first and watermark only the pages you need.
Where do I check the middle pages got watermarked?
Scroll to a page near the middle of the downloaded document.
How do I watermark a second document after this one?
Repeat the upload step with a new PDF file.
Where do I find the finished file?
Save the multi-page result once processing finishes.