GenerateFormAppearances method

Questa voce API conserva identificatori, firme, blocchi di codice e termini PDF nella forma originale.

Regenerates the /AP (appearance stream) for every form widget on every page by rendering each page through FPDF_FFLDraw. This is the recommended companion call to FormField[i] := value assignments — without it, form values may be visible only when the field has focus, and any subsequent flatten operation will silently lose the values. Call after all FormField[] assignments and before SaveAs / FlattenPage / FlattenAllPages.

GenerateFormAppearances rebuilds the /AP (appearance stream) entry for every AcroForm widget across all pages of the loaded document. It does this by rendering each page through the PDFium form-fill engine (FPDF_FFLDraw), which causes the current field values to be baked into the widget's visual representation stored inside the PDF file.

This call is a mandatory companion to FormField[i] := value assignments. Without it, a form field's value is stored in the PDF's data dictionary but has no corresponding appearance stream. PDF viewers typically show the value only while the field has input focus; other viewers may show nothing at all. More critically, any call to FlattenPage or FlattenAllPages without prior appearance generation will silently produce output that is missing the filled-in values.

The correct workflow when filling and locking a form is: assign all FormField[] values → call GenerateFormAppearances once → optionally call FlattenPage / FlattenAllPages → call SaveAs. If you only need to save the filled form without flattening, GenerateFormAppearances is still recommended to ensure maximum compatibility with third-party PDF viewers.

The procedure operates on the entire document in one call; there is no per-page variant.

FlattenPage, FlattenAllPages, FormField, SaveAs