You can search for a House Document number within the Internal Revenue Acts of the United States. Begin your searching by entering the Taxation & Economic Reform in American Parts I & II database and click on Internal Revenue Acts of the United States. From here choose the House Document Number option from the drop-down menu. You do not need to input the prefix H. Doc., only the document number itself.
Example: Search for H. Doc. 75-337
The results page should provide you with a link to the correct House document.