we're getting there

example/main.odin

@@ -1,7 +1,16 @@
 package pdf_example
 
+import "core:fmt"
+import "core:os"
+
 import pdf "../"
 
 main :: proc() {
-    pdf.open_file("example.pdf")
+    doc, err := pdf.open_file(os.args[1])
+    defer pdf.destroy_document(doc)
+    if err != nil {
+        fmt.panicf("Failed to open PDF file: %v", err)
+    }
+
+    fmt.println(doc)
 }

pdf.odin

@@ -1,12 +1,18 @@
 package pdf
 
 import "core:os"
+import "core:fmt"
+
+PDF_MAGIC :: "%PDF-"
 
 Error :: enum {
+    Ok,
     File_Read_Error,
+    InvalidFile,
 }
 
 Document :: struct {
+    version: string
 }
 
 open :: proc{
@@ -14,7 +20,7 @@ open :: proc{
     open_bytes,
 }
 
-open_file :: proc(path: string) -> (pdf: ^Document, err: Error) {
+open_file :: proc(path: string) -> (doc: ^Document, err: Error) {
     data, read_err := os.read_entire_file(path, context.allocator)
     if read_err != nil {
         return nil, .File_Read_Error
@@ -23,5 +29,18 @@ open_file :: proc(path: string) -> (pdf: ^Document, err: Error) {
     return open_bytes(data)
 }
 
-open_bytes :: proc(data: []u8) -> (pdf: ^Document, err: Error) {
+open_bytes :: proc(data: []u8) -> (doc: ^Document, err: Error) {
+    doc = new(Document)
+
+    if string(data[:5]) != PDF_MAGIC {
+        return nil, .InvalidFile
+    }
+
+    doc.version = string(data[5:5+3])
+
+    return doc, nil
+}
+
+destroy_document :: proc(pdf: ^Document) {
+    free(pdf)
 }