The PDF format is a robust and versatile medium for document exchange. However, not all PDFs are created equal, and issues with structure, compliance, or optimization can arise. Here, we’ll explore key parameters used by PDF Checker to evaluate and optimize PDFs for usability, compatibility, and efficiency. 

General Parameters

• Unable-to-Open Indicates the file is not a valid PDF or is corrupted to the point of being unreadable.  
• Password-Protected The file requires a password to open. Provide the password via a command line argument to proceed.  
• Contains-Owner-Password An owner password restricts editing, copying, or printing but allows viewing. Owner passwords help maintain document security and compliance.  
• XFA-Type and AcroForms-Type XFA Forms: Proprietary XML-based forms embedded within PDFs, primarily used with web forms. AcroForms: Widely compatible PDF forms supported by most applications.  
• PDF Version Identifies whether a document conforms to PDF 2.0 standards, introduced in 2017.  
• Contains-Signature Verifies the presence of digital signatures and checks their certification by a Certifying Authority.  
• PDF/A Compliance Checks the document’s archival standard conformance, such as:  
  • PDF/A-1b: Ensures visual appearance.  
  • PDF/A-2u: Adds Unicode mapping.  
  • PDF/A-3b: Allows embedding of non-PDF files.  
• PDF/X, PDF/E, PDF/VT, and PDF/UA Compliance Ensures compatibility for specific workflows like graphic exchange (PDF/X), engineering (PDF/E), variable printing (PDF/VT), or accessibility (PDF/UA).  
• Tagged PDF Checks for structural tags ensuring accessibility compliance and assistive software compatibility.  
• Image-Only PDFs Differentiates scanned image-based PDFs from standard PDFs, which affects OCR processing.  

Cleanup and Optimization Parameters

• Suboptimal Compression Identifies inefficient compression methods and optimizes file size.  
• Transparency Flattens transparent layers to improve rendering speed and compatibility.  
• Annotations Detects hidden, non-printable, or improperly rendered annotations.  
• Embedded Private Data Removes unnecessary private data to reduce file size and improve security.  

Fonts

• Non-Extractable Text Flags fonts that hinder text extraction or searching.  
• Embedded Fonts Checks if fonts are embedded for consistency across devices.  
• Font Descriptor Completeness Validates key metrics like CapHeight for proper font rendering.  

Images  

• Resolution Checks Flags images with resolutions outside specified ranges (e.g., below 150 DPI or above 600 DPI for color images).  
• JPEG2000 Compression Identifies images using advanced compression formats for potential optimization.  
• Alternate Images Scans for unnecessary alternate images that bloat file size.  

Metadata and Embedded Files

• Document Metadata Identifies and optionally removes metadata like author, creation date, and software used.  
• Embedded Files Detects and removes embedded attachments to reduce file size.    

PDF Checker offers a comprehensive suite of tools to analyze and optimize your PDF documents. From ensuring compliance to improving accessibility and reducing file size, these parameters help create efficient, user-friendly, and secure documents.