Font size zero in fillable multiline-input-field in PDF-Form

Question

I got stuck with a PDF-Document, which (among other fields) contains five larger multiline text inputs. For all five fields, the DefaultAppearance-parameter of the relevant widget says the following.

/DA (/SimplonNorm 0 Tf 0 g)

Is this a bug, a feature, or an unintended slip by the person who designed this PDF-Form?

This zero font size would result in the invisible text once the document gets printed. To my observation, different PDF-viewers/writers (firefox,chromium,ubuntu-document-viewer) seem to substitute this zero-value by an obviously arbitrary new font-size. This, in turn, results in the different rendering of the input field, depending on the tool by means of which the form fields get filled.

I am working on a PHP tool to fill this form automatically, and a bit unsure whether I choose an arbitrary value myself or whether we should additionally contact the government agency that designed it.

Answer 1

A 0 as font size in the default appearance string is specified as follows:

A zero value for size means that the font shall be auto-sized: its size shall be computed as an implementation dependent function.

(ISO 32000-2 section 12.7.4.3 "Variable text")

The idea is to use the largest font size value for which the text still fits into the text field. Due to different type setting algorithms for form fields in different viewers, though, the result is implementation dependent.

Thus, your observation

To my observation, different PDF-viewers/writers (firefox,chromium,ubuntu-document-viewer) seem to substitute this zero-value by an obviously arbitrary new font-size. This, in turn, results in different rendering of the input-field, depending on the tool by means of which the form-fields get filled.

exactly is to be expected.