Is there a file limit in Acrobat Actions?

Greeting!

Dear StavrosD,

Yes, there is a file limit when using Acrobat Actions. The specific file limit may vary depending on the version of Adobe Acrobat or Adobe Acrobat Pro you are using. Generally, Acrobat Actions allow you to process multiple files simultaneously, but there may be practical limits based on factors such as file size, available system resources, and the complexity of the actions being performed. To ensure optimal performance and avoid potential issues, it is recommended to keep the number of files within a reasonable range and consider the capabilities of your computer or server. If you encounter any limitations or performance issues while using Acrobat Actions, you may need to adjust the number or size of the files being processed or consider alternative solutions, such as batch processing or dividing the files into smaller batches. For more specific information about file limits and capabilities related to Acrobat Actions, it is advisable to refer to the official documentation or reach out to Adobe support for assistance.

The other thing to beware of is that folders with many files can be very slow (much slower than just adding together times might imagine). Could take hours just to get a file list in any app. You have a big job, I don't envy you...

This often happens. Find an automation tool for basic interactive use, leap to using it for thousands of files. No, you need tools made for volume automation. If your company policy forbids getting the right tool, subdivide the work into about 200 files at a time, restarting Acrobat after each batch.

You also need to do estimates of time not just hope it will finish overnight. For example, if an average file takes 10 seconds, then doing 500,000 would take 2 months. 

500.000 files are too much for an action.