FitMode property

FitMode is the standard PDF-viewer fit-page / fit-width selector exposed as a published property so applications can drop a TPdfView onto a form and pick a layout without writing zoom math. Each value maps onto a clear visual behavior:

• pfmNone — manual zoom. Whatever Zoom the application or end user sets is honored exactly. This is the default to preserve pre-v1.19.0 behavior for existing applications.
• pfmActualSize — 100%. Renders one PDF user unit (1/72 inch) per CSS pixel.
• pfmFitPage — the whole page fits inside the viewport. The view picks the smaller of the page-width-fit and page-height-fit zooms.
• pfmFitWidth — the page width matches the viewport width; height scrolls. Good for long documents read top to bottom.

The active fit mode is re-applied automatically when the control is resized and when the current page changes — that is the whole point of FitMode versus a one-shot zoom assignment. Long documents with mixed page sizes (a portrait cover followed by landscape spreads, for example) stay perfectly framed without any extra Resize / OnPageChange handler.

Setting Zoom directly cancels the active fit mode and reverts FitMode to pfmNone, matching the standard PDF viewer convention where typing a zoom percentage drops out of "Fit Page" / "Fit Width". This keeps the property value honest: FitMode <> pfmNone means "the view will re-fit on the next layout event".

• FitMode does NOT cache the chosen Zoom — the math runs every time the active fit mode is re-applied, so swapping rotation, resizing the window, or paging to a differently sized page always produces the correct zoom.
• Combine FitMode = pfmFitWidth with SmoothScroll for the classic "long-document reader" feel.
• If the host application wants to expose a "Fit Page" / "Fit Width" button bar, just assign FitMode — no extra Zoom computation needed.