The reason for a PDF file not to open on a computer can either be a problem with the PDF file itself, an issue with password protection or non-compliance with industry standards. It could also be an issue with the PDF reader being used, Acrobat or operating system settings.
PDF files cannot be opened when the files are damaged or corrupted internally. Password protection can also restrict a PDF file from opening, particularly if the password is unknown. In addition, some PDF file creators do not adhere to the standards that the majority of PDF readers and/or Acrobat expect, thereby causing the files they create not to be recognized by these programs. Lastly, a PDF file may not open correctly if the reader has not been updated, repaired or installed properly.