Merge pull request #16 from ycexiao/refactor-pdfadapter

refactor: change the `PDFAdapter` interface to allow modular interactions

Author: sbillinge

news/refactor-pdfadapter.rst

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+**Added:**
+
+* <news item>
+
+**Changed:**
+
+* Refactored ``PDFAdapter``.
+
+**Deprecated:**
+
+* <news item>
+
+**Removed:**
+
+* <news item>
+
+**Fixed:**
+
+* <news item>
+
+**Security:**
+
+* <news item>