PDF 疊加

Type a range in the Apply to pages field using the base document's page numbers, for example 1-5, 8, 10-z, where z stands for the last page. Leave it empty to cover every page.

With the loop option on, the overlay's pages repeat in order until every base page is covered, so a 2-page overlay on a 5-page document is applied as 1, 2, 1, 2, 1. With it off, pages are matched one to one and base pages beyond the overlay's length are left unchanged.

No. An overlay page larger than the base page is scaled down to fit and a smaller one is centered without being enlarged. There are no controls for position, scale, or opacity, so build the overlay PDF at the size and transparency you want before combining.

Yes. The base document's text, links, form fields, and bookmarks are untouched; the overlay is added to each page as an extra drawing layer, and any text in it remains selectable too.

No. Only the visible page content of the overlay is used. Annotations on the overlay pages, including links, form fields, and comments, don't transfer to the result.

Underlay, so the letterhead sits behind the page content, with the loop option on if the letterhead is a single page. For text or image watermarks with adjustable opacity, rotation, and placement, Add Watermark gives more control.

The tool doesn't ask for passwords. If either file needs a password to open, remove it first with the password removal tool, then apply the overlay to the copy without the password.

No. The overlay is applied by qpdf compiled to WebAssembly, which runs entirely in your browser, so neither the base document nor the overlay file leaves your device. The combined PDF downloads under the base document's filename.