Proof of concept to replace PDF form fields' font

PDF form fields are `/DA` fields (PDF Reference page 534,
https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/pdf_reference_archives/PDFReference.pdf).

Get all `/DA` objects. Their value is a string that specifies the
field's appearance properties. One part of the appearance string is the
font name (its Postscript name). By replacing the font name with a
different one, we can change the field's font.

4 files changed, 590 insertions, 0 deletions

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diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..990d62e
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "pdf-font"
+version = "0.1.0"
+edition = "2018"
+
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diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..91e1a0e
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,36 @@
+use lopdf::{Document, Object};
+
+
+fn main() {
+    let mut doc = Document::load("./f1040.pdf").unwrap();
+
+    for (_, mut obj) in &mut doc.objects {
+        // println!("{:?}", obj);
+
+        match &mut obj {
+            Object::Dictionary(ref mut d) => {
+                for (k, v) in d.iter_mut() {
+                    let key = std::str::from_utf8(k).unwrap();
+
+                    if key == "DA" {
+                        // println!("{:?}", d);
+
+                        let properties = v.as_str_mut().unwrap();
+
+                        let new_properties = std::str::from_utf8(properties)
+                            .unwrap()
+                            .replace("HelveticaLTStd-Bold", "CourierNewPSMT");
+
+                        *properties = new_properties.into_bytes();
+
+                        dbg!(std::str::from_utf8(properties).unwrap());
+                        // dbg!(properties);
+                    }
+                }
+            },
+            _ => (),
+        }
+    }
+
+    doc.save("./new.pdf").unwrap();
+}