Reasons  won't your computer open PDF file Steps to  fix it:

• Download and install the most recent version of Adobe Acrobat.-If you're using an old version of Adobe Acrobat, it might not be able to open all of your PDF files. Adobe's Acrobat and Reader programmes are updated on a regular basis. As a result, recommend that you get the software through Adobe's official download page. Select the current OS system version and click the Download Now button while you're there.
•  At startup, disable the Protected mode.
• If the file is damaged, request that the sender transmit it again.-This isn't a typical issue, but it's conceivable that the PDF file wasn't created perfectly by the programme that created it. The PDF file may also include corrupt data at times. The simplest approach to determine this is to open another PDF file and see if it opens; if it does, the file in question is damaged. The simplest solution is to request that the file be resent from the sender.
• For non-compliant PDFs, revert to an earlier version.
• Installation of the application should be repaired.

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